International Law by Jan Klabbers (z-lib.org)

International Law

Written by one of the world's leading international lawyers, this is a landmark publication in the
teaching of international law. International law can be defined as ‘the rules governing the legal
relationship between nations and states’, but reality is much more complex, with political, diplomatic
and socio-economic factors shaping the law and its application. This refreshingly clear, concise
textbook encourages students to view international law as a dynamic system of organizing the world.
Bringing international law back to its first principles, the book is organized around four questions.
Where does it come from? To whom does it apply? How does it resolve conflict? What does it say?
Building on these questions with both academic rigour and clarity of expression, Professor Klabbers
breathes life and energy into the subject. Footnotes point students to the wider academic debate while
chapter introductions and final remarks reinforce learning.

Jan Klabbers is Professor of International Law at the University of Helsinki. He has held visiting
professorships at Hofstra University (New York, 2007), the Graduate Institute of International and
Development Studies (Geneva, 2008) and the University of Paris (Panthéon-Assas, 2011), and was
one of the Inaugural Fellows at the Straus Institute for the Advanced Study of International Law and
Justice at New York University (2009–10). He served as Director of the Academy of Finland Centre
of Excellence in Global Governance Research 2006–11.

International Law

Jan Klabbers

CAMBRIDGE UNIVERSITY PRESS
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi, Mexico City

Cambridge University Press
The Edinburgh Building, Cambridge CB2 8RU, UK
Published in the United States of America by Cambridge University Press, New York

www.cambridge.org
Information on this title: www.cambridge.org/9780521194877

© Jan Klabbers 2013

This publication is in copyright. Subject to statutory exception and to the provisions of relevant
collective licensing agreements, no reproduction of any part may take place without the written

permission of Cambridge University Press.

First published 2013
Printed and bound in the United Kingdom by the MPG Books Group
A catalogue record for this publication is available from the British Library

Library of Congress Cataloguing in Publication data
Klabbers, Jan.

International law / Jan Klabbers.
pages cm

Includes bibliographical references and index.
ISBN 978-0-521-19487-7 (hardback) – ISBN 978-0-521-14406-3 (paperback)
1. International law. 2. International law – Political aspects. 3. International law – Social aspects. 4.

International law – Economic aspects. I. Title.
KZ3410.K57 2013

341 – dc23 2012034003
ISBN 978-0-521-19487-7 Hardback
ISBN 978-0-521-14406-3 Paperback

Cambridge University Press has no responsibility for the persistence or accuracy of URLs for
external or third-party internet websites referred to in this publication and does not guarantee that

any content on such websites is, or will remain, accurate or appropriate.

Contents

Detailed table of contents
Table of cases
Preface
List of abbreviations
Part I The structure of international law
1 The setting of international law
2 The making of international law
3 The law of treaties
4 The subjects of international law
5 Jurisdiction, powers and immunities
6 The individual in international law
7 The law of responsibility
8 International courts and tribunals
9 Sanctions, countermeasures and collective security
Part II The substance of international law
10 Use of force
11 The law of armed conflict
12 International criminal law
13 The seas, the air and outer space
14 Protecting the environment
15 The global economy
Part III The surroundings of international law
16 Domestic courts and their relationship with international law
17 The politics and ethics of international law and global governance
18 By way of conclusion
Bibliography
Index

Detailed table of contents

Table of cases
Preface
List of abbreviations
Part I The structure of international law
1 The setting of international law

Introduction
The seventeenth century
Colonialism
International law and the global economy
The international legal system
International legal theories
International law in international relations theory
Globalization, global governance and international law
Ethics and international law
Final remarks: a critical perspective
2 The making of international law
Introduction
Two ships (or perhaps three): Lotus and Wimbledon
Article 38 Statute ICJ
Treaties
Customary law

A general practice
Accepted as law
The method of custom: the Paquete habana
Consent and the persistent objector
A normative problem, or towards modern custom
On law-breaking and law-making
General principles of law
Unilateral declarations
Other possible sources and the renewal of sources doctrine
Final remarks
3 The law of treaties
Introduction
Two basic principles
The concept of treaty
The conclusion of treaties
Reservations
Interpretation
The application of treaties
Treaty revision
Validity and invalidity
Termination and suspension
Final remarks
4 The subjects of international law
Introduction
States

Population
Territory
Effective government
Capacity to enter into international relations
Recognition of states (or governments)
Acquisition of territory
Internationalized territory
Statehood: continuity and change
International organizations
The United Nations
Other subjects
Final remarks
5 Jurisdiction, powers and immunities
Introduction
Five principles
Territoriality
Nationality
Protection
Passive personality
Universality
Extraterritorial jurisdiction
Concurrent jurisdiction
The powers of international organizations
Sovereign immunities
Heads of state and others
Diplomatic privileges and immunities
Final remarks
6 The individual in international law
Introduction
From slavery to human rights
The institutionalization of human rights
The application of human rights
Group rights
Self-determination
Nationality
The right to have rights? Stateless persons, refugees and migrants
Final remarks
7 The law of responsibility
Introduction
From custom to codification
State responsibility: two basic principles
Attribution
Internationally wrongful act
Responsibility and private acts
Circumstances precluding wrongfulness
Consequences of responsibility
Responsible to whom?
Responsibility of international organizations
Individual responsibility
Shared responsibility?
Final remarks

8 International courts and tribunals
Introduction
Settling disputes
Arbitration
Adjudication and the ICJ
Jurisdiction
All cases which the parties refer to it
All matters specially provided for in the Charter
All matters specially provided for…in treaties and conventions in force
The optional clause
Transferred jurisdiction
Forum prorogatum
Admissibility
Exhaustion of local remedies
The nationality of complaints
Interim measures of protection
Compensation
Miscellaneous issues
Non-appearance
Third parties and the Court
Advisory opinions
Judicial review?
Final remarks

9 Sanctions, countermeasures and collective security
Introduction
Inadimplenti non est adimplendum
Retorsion
Reprisals and countermeasures
Collective security
Triggering collective action
The role of the General Assembly
Peacekeeping
Individual sanctions
Limits to the Security Council?
Final remarks

Part II The substance of international law
10 Use of force

Introduction
Abolishing war
The UN Charter
Self-defence
Humanitarian intervention
Terrorism
The end of armed conflict
Final remarks
11 The law of armed conflict
Introduction
International humanitarian law
International and non-international conflicts
Proportionality and military necessity
Arms and weapons

International humanitarian law and international organizations
International humanitarian law and privatization
Foreign occupation
Jus post bellum and post-conflict governance
Wars against phenomena
Final remarks
12 International criminal law
Introduction
War crimes trials and the ICC
Core crimes
Individual responsibility
Transboundary police cooperation
Extradition
Abduction and deportation
Final remarks
13 The seas, the air and outer space
Introduction
Outline of the maritime regime
Internal waters
Territorial sea and contiguous zone
Exclusive economic zone (EEZ)
Continental shelf
High seas
The deep seabed
Maritime delimitation
Air law
Space law
Final remarks
14 Protecting the environment
Introduction
Early case-law
Pulp Mills
Specific issues
Proceduralization and institutionalization
Compliance procedures
Final remarks
15 The global economy
Introduction
Private international law
International taxation
Financial institutions
World trade and the WTO
Investment protection
Economic ‘soft law’
Development and a New International Economic Order
Final remarks
Part III The surroundings of international law
16 Domestic courts and their relationship with international law
Introduction
Monism and dualism
Direct effect

Incorporating international law
The special case of the EU
Towards a new dualism?
Avoidance strategies
Final remarks
17 The politics and ethics of international law and global governance
Introduction
Global governance
The politics of international law
Global ethics
Towards virtue?
Final remarks
18 By way of conclusion
Bibliography
Index

Table of cases

Badinter Commission

Opinion no. 1, 29 November 1991.
Opinion no. 3, 11 January 1992.
Reactions, 26 May 1993.

Conciliation Commission

Jan Mayen Conciliation Commission, 19–20 May 1981.

Court of Justice of the European Union (CJEU)

A. Racke GmbH & Co. v. Hauptzollamt Mainz, Case C-162/96, [1998] ECR I-3655.
Ahlström and others v. Commission, Joined cases 89, 104, 114, 116, 117 and 125–129/85, [1988]

ECR 5193 (Woodpulp).
Defrenne v. Sabena, Case 43/75, [1976] ECR 455.
France v. Commission, Case C-233/02, [2004] ECR I-2759.
Kadi and Al Barakaat v. Council and Commission, Joined cases C-402/05 P and C-415/05 P,

[2008] ECR I-6351.
Van Gend & Loos v. Netherlands Internal Revenue Administration, Case 26/62, [1963] ECR 1.

Domestic courts

Australia

Mabo and Others v. Queensland (no. 2), High Court, 3 June 1992.

Canada

Re Secession of Quebec, Supreme Court, 20 August 1998.

Italy

Ferrini v. Federal Republic of Germany, Court of Cassation, Italy, 11 March 2004.

Japan

Shimoda et al. v. The State, Tokyo District Court, 1963.

South Africa

Government of the Republic of South Africa and others v. Irene Grootboom and others,
Constitutional Court, 4 October 2000.

United Kingdom

Regina v. Bow Street Metropolitan Stipendiary Magistrate, ex parte Pinochet Ugarte (no. 3).
Regina v. Horseferry Road Magistrates Court, ex parte Bennett.

United States

Banco Nacional de Cuba v. Sabbatino, 376 US 398, US Supreme Court, 23 March 1964.
Boumediene v. Bush, 553 US 723, US Supreme Court, 12 June 2008.
Filártiga v. Peña-Irala, 630 F.2d 876, Second Circuit Court of Appeals, 30 June 1980.
Foster v. Neilson, 27 US 253, US Supreme Court, January 1829.
Hamdan v. Rumsfeld, 548 US 557, US Supreme Court, 29 June 2006.
Medellín v. Texas, 552 US 1, US Supreme Court, 25 March 2008.
Paquete Habana, 175 US 677, US Supreme Court, 8 January 1900.
Princz v. Federal Republic of Germany, 26 F.3d 1166, US DC Circuit Court of Appeals, 1 July

1994.
Siderman de Blake v. Argentina, 965 F.2d 669, US Ninth Circuit Court of Appeals, 22 May 1992.
Sosa v. Humberto Alvarez-Machaín, 542 US 692, US Supreme Court, June 29, 2004.
Tel-Oren v. Libyan Arab Republic, 726 F.2d 774, US DC Circuit Court of Appeals, 3 February

1984.
United States v. Alvarez-Machaín, 504 US 655, US Supreme Court, 15 June 1992.

In re Yamashita, US Military Commission, 7 December 1945.
In re Yamashita, US Supreme Court, 4 February 1946.

European Court of Human Rights (ECtHR)

Al-Skeini and Others v. United Kingdom (Application no. 55721/07) 7 July 2011.
Bankovic and others v. Belgium and others, admissibility (Application no. 52207/99), decision

of 12 December 2001.
Behrami and Behrami v. France (Application no. 71412/01), and Saramati v. France and

others (Application no. 78166/01), decision of 2 May 2007.
Belilos v. Switzerland (Application no. 10328/83), 29 April 1988.
Golder v. United Kingdom (Application no. 4451/70), 21 February 1975.
Handyside v. United Kingdom (Application no. 5493/72), 7 December 1976.
Loizidou v. Turkey, preliminary objections (Application no. 15318/89), 23 March 1995.
McCann and others v. United Kingdom (Application no. 18984/91), 27 September 1995.
Saramati v. France see Behrami and Behrami.
Streletz, Kessler and Krenz v. Germany (Application nos. 34044/96, 35532/97 and 44801/98), 22

March 2001.

GATT/WTO

United States – Measures Concerning the Importation, Marketing and Sale of Tuna and Tuna
Products, WTO, DS381, panel report circulated 15 September 2011.

United States – Restrictions on Import of Tuna, DS21R-39S155.

General Court (EU, formerly Court of First Instance)

Kadi v. Council, Case T-315/01, [2005] ECR II-3649.
Opel Austria GmbH v. Council, Case T-115/94, [1997] ECR II-39.

International arbitral awards

Air Services Agreement of 27 March 1946, award of 9 December 1978.
Alabama Claims, arbitration, Washington, DC: US Government Printing Office 1898 (reprinted

in Moore, International Arbitration, I, 653–9).
Anglo-French Continental Shelf, arbitration, award of 30 June 1977.
Bering's Sea, arbitration (USA/UK), award of 15 August 1893.
Island of Palmas case (US v. Netherlands), award of 4 April 1928.
Lake Lanoux, arbitration (France v. Spain), award of 16 November 1957.
Petroleum Development Ltd v. Sheikh of Abu Dhabi, award of September 1951.
Naulilaa (Portugal v. Germany), Special Arbitral Tribunal, 31 July 1928.
Rainbow Warrior (New Zealand v. France), 30 April 1990.
Texaco Overseas Petroleum Company and California Asiatic Oil Company v. Libya, merits.
Trail Smelter (USA/Canada), 11 March 1941.

International Court of Justice

Accordance with International Law of the Unilateral Declaration of Independence in Respect of
Kosovo, advisory opinion, 22 July 2010, nyr.

Aegean Sea Continental Shelf (Greece v. Turkey), jurisdiction, [1978] ICJ Reports 3.
Aerial Herbicide Spraying (Ecuador v. Colombia), pending.
Aerial Incident of October 7th, 1952 (USA v. USSR), Order, [1956] ICJ Reports 9.
Aerial Incident of March 10th, 1953 (USA v. Czechoslovakia), Order, [1956] ICJ Reports 6.
Aerial Incident of September 4th, 1954 (USA v. USSR), Order [1958] ICJ Reports 158.
Aerial Incident of 7 November 1954 (USA v. USSR), Order, [1959] ICJ Reports 276.
Aerial Incident of July 27, 1955 (Israel v. Bulgaria), preliminary objections, [1959] ICJ Reports
127.
Aerial Incident of 27 July 1955 (USA v. Bulgaria), Order, [1960] ICJ Reports 146.
Aerial Incident of 27 July 1955 (UK v. Bulgaria), Order, [1959] ICJ Reports 264.
Aerial Incident of 3 July 1988 (Iran v. US), Order [1996] ICJ Reports 9.

Ahmadou Sadio Diallo (Republic of Guinea v. Democratic Republic of Congo), judgment of 30
November 2010, nyr.

Ambatielos (Greece v. United Kingdom), preliminary objections, [1952] ICJ Reports 28.

Applicability of Article VI, Section 22, of the Convention on the Privileges and Immunities of the
United Nations, [1989] ICJ Reports 177.

Application of the Convention on the Prevention and Punishment of the Crime of
Genocide (Bosnia and Herzegovina v. Serbia and Montenegro), further requests for the indication of
provisional measures, [1993] ICJ Reports 325.

Application of the Convention on the Prevention and Punishment of the Crime of
Genocide (Bosnia and Herzegovina v. Serbia and Montenegro), [2007] ICJ Reports 43.

Application of the International Convention on the Elimination of All Forms of Racial
Discrimination (Georgia v. Russian Federation), preliminary objections, judgment of 1 April 2011,
nyr.

Application for Revision and Interpretation of the Judgment of 24 February 1982 in the Case
concerning the Continental Shelf (Tunisia/Libyan Arab Jamahiriya) (Tunisia v. Libya), [1985] ICJ
Reports 192.

Armed Activities on the Territory of the Congo (Democratic Republic of Congo v. Burundi),
Order, [2001] ICJ Reports 3.

Armed Activities on the Territory of the Congo (Democratic Republic of Congo v. Rwanda),
Order, [2001] ICJ Reports 6.

Armed Activities on the Territory of the Congo (Democratic Republic of Congo v. Uganda),
[2005] ICJ Reports 168.

Armed Activities on the Territory of the Congo (New Application: 2002) (Democratic Republic
of Congo v. Rwanda), jurisdiction and admissibility, [2006] ICJ Reports 6.

Arrest Warrant of 11 April 2000 (Democratic Republic of Congo v. Belgium), [2002] ICJ Reports
3.

Asylum (Colombia/Peru), [1950] ICJ Reports 266.

Avena and Other Mexican Nationals (Mexico v. USA), [2004] ICJ Reports 12.

Barcelona Traction, Light and Power Company, Limited (Belgium v. Spain), [1970] ICJ Reports
3.

Border and Transborder Armed Actions (Nicaragua v. Costa Rica), Order, [1987] ICJ Reports
182.

Border and Transborder Armed Actions (Nicaragua v. Honduras), Order, [1992] ICJ Reports
222.

Certain Expenses of the United Nations (Article 17, Paragraph 2, of the Charter), advisory
opinion, [1962] ICJ Reports 151.

Certain Norwegian Loans (France v. Norway), [1957] ICJ Reports 9.

Certain Questions of Mutual Assistance in Criminal Matters (Djibouti v. France), [2008] ICJ
Reports 177.

Continental Shelf (Tunisia/Libya), [1982] ICJ Reports 18.

Continental Shelf (Libya/Malta), [1985] ICJ Reports 13.

Corfu Channel preliminary objections, [1948] ICJ Reports 15.

Corfu Channel, merits, [1949] ICJ Reports 4.

Corfu Channel, assessment of the amount of compensation, [1949] ICJ Reports 244.

Delimitation of the Maritime Boundary in the Gulf of Maine Area (Canada/United States), [1984]
ICJ Reports 246.

Difference Relating to Immunity from Legal Process of a Special Rapporteur of the Commission
on Human Rights, [1999] ICJ Reports 62.

Dispute Regarding Navigational and Related Rights (Costa Rica v. Nicaragua), judgment of 13
July 2009, nyr.

East Timor (Portugal v. Australia), [1995] ICJ Reports 90.

Effect of Awards of Compensation made by the United Nations Administrative Tribunal, advisory
opinion, [1954] ICJ Reports 47.

Elettronica Sicula SpA (ELSI) (USA v. Italy), [1989] ICJ Reports 15.

Fisheries (United Kingdom v. Norway), [1951] ICJ Reports 116.

Fisheries Jurisdiction (Germany v. Iceland), [1973] ICJ Reports 49.

Fisheries Jurisdiction (Spain v. Canada), jurisdiction, [1998] ICJ Reports 432.

Fisheries Jurisdiction (UK v. Iceland), jurisdiction, [1973] ICJ Reports 3.

Frontier Dispute (Burkina Faso/Mali), [1986] ICJ Reports 554.

Gabcikovo-Nagymaros Project (Hungary/Slovakia), [1997] ICJ Reports 7.

Interhandel (Switzerland v. United States), preliminary objections, [1959] ICJ Reports 6.

Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt, advisory opinion,
[1980] ICJ Reports 73.

Jurisdiction and Enforcement of Judgments in Civil and Commercial
Matters (Belgium v. Switzerland), Order of 5 April 2011, nyr.

Jurisdictional Immunities of the State (Germany v. Italy; Greece Intervening), judgment of 3
February 2012, nyr.

LaGrand (Germany v. USA), [2001] ICJ Reports 466.

Land, Island and Maritime Frontier Dispute (El Salvador/Honduras), application by Nicaragua
for permission to intervene, [1990] ICJ Reports 92.

Land and Maritime Boundary between Cameroon and Nigeria (Cameroon v. Nigeria),
application to intervene, Order, [1999] ICJ Reports 1029.

Land and Maritime Boundary between Cameroon and Nigeria (Cameroon v. Nigeria; Equatorial
Guinea intervening), [2002] ICJ Reports 303.

Legal Consequences for States of the Continued Presence of South Africa in Namibia (South West
Africa) notwithstanding Security Council Resolution 276 (1970), advisory opinion, [1971] ICJ
Reports 16.

Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, advisory
opinion, [2004] ICJ Reports 136.

Legality of the Threat or Use of Nuclear Weapons, advisory opinion, [1996] ICJ Reports 226.

Legality of Use of Force (Serbia and Montenegro v. Belgium), [2004] ICJ Reports 279.

Legality of the Use by a State of Nuclear Weapons in Armed Conflict, advisory opinion, [1996]
ICJ Reports 66.

Maritime Delimitation and Territorial Questions between Qatar and Bahrain (Qatar v. Bahrain),
jurisdiction and admissibility, [1994] ICJ Reports 112.

Maritime Delimitation in the Black Sea (Romania v. Ukraine), [2009] ICJ Reports 61.

Minquiers and Ecrehos (France/United Kingdom), [1953] ICJ Reports 47.

Military and Paramilitary Activities In and Against Nicaragua (Nicaragua v. USA), Jurisdiction
of the Court and Admissibility of the Application, [1984] ICJ Reports 392.

Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. USA), merits,
[1986] ICJ Reports 14.

North Sea Continental Shelf (Germany/Denmark; Germany/Netherlands), [1969] ICJ Reports 3.

Nottebohm (Second Phase), (Liechtenstein v. Guatemala), [1955] ICJ Reports 4.

Nuclear Tests (Australia v. France), [1974] ICJ Reports 253.

Nuclear Tests (New Zealand v. France), [1974] ICJ Reports 457.

Oil Platforms (Iran v. USA), [2003] ICJ Reports 161.

Pulp Mills on the River Uruguay (Argentina v. Uruguay), judgment of 20 April 2010, nyr.

Questions of Interpretation and Application of the 1971 Montreal Convention Arising from the
Aerial Incident at Lockerbie (Lybia v. USA), Order, [1992] ICJ Reports 114.

Questions of Interpretation and Application of the 1971 Montreal Convention Arising from the
Aerial Incident at Lockerbie (Libya v. USA), Order, [2003] ICJ Reports 152.

Reparation for Injuries Suffered in the Service of the United Nations, advisory opinion, [1949]
ICJ Reports 174.

Request for Interpretation of the Judgment of 15 June 1962 in the Case Concerning the Temple
of Preah Vihear (Cambodia v. Thailand), Order of 18 July 2011, nyr.

Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide,
advisory opinion, [1951] ICJ Reports 15.

Right of Passage over Indian Territory (Portugal v. India), [1960] ICJ Reports 6.
South West Africa (Ethiopia v. South Africa; Liberia v. South Africa), preliminary objections,
[1962] ICJ Reports 319.
South West Africa (Ethiopia v. South Africa; Liberia v. South Africa), Second Phase, [1966] ICJ
Reports 6.
Temple of Preah Vihear (Cambodia v. Thailand), [1962] ICJ Reports 6.
United States Diplomatic and Consular Staff in Tehran (USA v. Iran), [1980] ICJ Reports 3.
Vienna Convention on Consular Relations (Paraguay v. USA), Order, [1998] ICJ Reports 248.
Western Sahara, advisory opinion, [1975] ICJ Reports 12.

International Criminal Court (ICC)

Prosecutor v. Thomas Lubanga Dyilo, ICC-01/04–01/06.

International Criminal Tribunal for the Former Yugoslavia (ICTY)

Prosecutor v. Dusko Tadic, Case IT-94–1.
Prosecutor v. Dusko Tadic, Case IT-94–1-A.
Prosecutor v. Radislav Krstic, Case IT-98–33-T.

International Tribunal for the Law of the Sea (ITLOS)

Responsibilities and Obligations of States Sponsoring Persons and Entities with Respect to Activities
in the Area, advisory opinion, ITLOS, 1 February 2011.

Permanent Court of International Justice (PCIJ)

Diversion of Water from the Meuse, [1937] Publ. PCIJ, Series A/B, no. 70.
Factory at Chorzów (Claim for Indemnity) (Germany v. Poland), merits, [1928] Publ. PCIJ,

Series A, no. 17.
Interpretation of the Greco-Turkish Agreement of December 1st, 1926, advisory opinion, [1928]

Publ. PCIJ, Series B, no. 16.
Jurisdiction of the Courts of Danzig, advisory opinion, [1928] Publ. PCIJ, Series B, no. 15.
Legal Status of Eastern Greenland, [1933] Publ. PCIJ, Series A/B, no. 53.
Mavrommatis Palestine Concessions, [1924] Publ. PCIJ, Series A, no. 2.
Nationality Decrees Issued in Tunis and Morocco (French Zone), advisory opinion, [1923] Publ.

PCIJ, Series B, no. 4.
Oscar Chinn, [1934] Publ. PCIJ, Series A/B, no. 63.
Payment in Gold of the Brazilian Federal Loans Issued in France, [1929] Publ. PCIJ, Series A,

no. 21.
Payment of Various Serbian Loans Issued in France, [1929] Publ. PCIJ, Series A, no. 20.
SS Lotus, [1927] Publ. PCIJ, Series A, no. 10.
SS Wimbledon, [1923] Publ. PCIJ, Series A, no. 1.
Status of Eastern Carelia, [1923] Publ. PCIJ, Series B, no. 5.
Territorial Jurisdiction of the International Commission of the River Oder (UK and

others v. Poland), [1929] Publ. PCIJ, Series A, no. 23.

UN Human Rights Committee

Sandra Lovelace v. Canada, Communication no. 24/1977, 30 July 1981

Preface

This book has been a long time in the making. While the actual writing started in 2009 and took place,
intermittently, until May 2012, the book reflects more than twenty years of teaching international
law. The basic premise underlying it is that international law should not be studied as a vast and ever-
increasing collection of rules, but is better approached as a way of thinking about and organizing the
world. With that in mind, like all legal systems the international legal order can profitably be studied
by asking four questions. First, there is the question of where the law comes from: what are its
sources? Second, to what entities or individuals does the law apply or, in other words, what are its
subjects? Third, what does the law do in cases of conflict (i.e. settlement), and finally, what does the
law actually say? What is its substance?

This book is organized with those four questions in mind. The first three, together pointing to the
basic structure of the system, make up Part I of this book (Chapters 1–9): sources, subjects and
settlement, broadly conceived. This is the stuff all international lawyers (probably even all lawyers,
in these days of globalization) will sooner or later be confronted with; all lawyers need to have some
idea of how international law is made, in what circumstances states can be held responsible, how
international tribunals function and whether or not specific entities are subject to international law.

The fourth question, asking about the substantive rules, makes up Part II (Chapters 10–15). It will
be noticed that Part I is longer and more analytical than Part II. This is only natural: the most Part II
can aspire to is to provide a basic description of the various branches of international law, without
much detail. After all, international law spans, quite literally, the world, as well as most of the policy
issues that one can think of. There is international law on topics as wide and diverse as international
crime, international investment, international taxation, the movement of refugees, the protection of
the environment and much, much more. Hence, a book such as this, limited in scope, can only cover
the basics. Fortunately though, there are wide bodies of literature available, as the footnotes testify,
and for those who want more detailed generalist expositions there are at least three useful larger and
more detailed general textbooks on the market. The interested reader could do worse than to pick one
of these to read alongside the present book.1

While Parts I and II cover the four questions set out above (sources, subjects, settlement and
substance), the book does not stop after Part II. It also contains a, fairly brief, Part III
(Chapters 16 and 17), addressing the context of international law. This addresses the circumstance
that international law does not exist in a vacuum, but is closely related, on the one hand, to national
legal systems (discussed in Chapter 16) and, on the other hand, to global governance, politics and
ethics (discussed in Chapter 17). As Joseph Weiler once suggested during a round-table discussion at
New York University, present-day textbooks on international law should ideally reflect the
circumstance that international law is part of a broader pattern of global governance, and not stick to
describing a stilted world where all legally relevant rules are made by duly empowered diplomats,
representing sovereign states. In Weiler's words, global governance ‘is a coloring agent that suddenly
illuminates phenomena that, under the normal spectacle of international law, you didn't see’.2 This
book hopes to reflect the two ideas that international law is of relevance to global governance, but
sometimes struggles to come to terms with it. However, the format of this book does not allow for an
in-depth discussion of the political context of international law: Part III remains necessarily brief.

Readers with an interest in these matters may be well advised to read this book alongside a recent
collection of articles edited by Crawford and Koskenniemi.3

This is a textbook on international law, and this simple fact has at least two important
implications. First, since the aim is to outline the international legal order, the book is not set up as a
commentary on current events. I accept that the reader may wish to see how the law is applied to
specific events, and where possible this has been done, but without singling out specifically current
events. Such comments on current events as there are serve purely illustrative purposes, if only
because current events tend to have a limited shelf-life; what is current today may be forgotten
tomorrow.

Second, this is a book on international law, and while there is room for the argument that the EU
is part of international law, it does not address the EU separately, except where the practice of the EU
is of relevance. Thus, there are fragments on the treaty practice of the EU, and a few paragraphs on
the attitude of the EU to international law, but no detailed discussion of EU law, if only because
others are far better qualified to discuss the EU than I am.4

Finally, a note on sources. I have generally refrained from listing the specific places where treaties
or other instruments can be found, for the solid reason that these instruments are easier to find these
days by a quick internet search than by going through the volumes of the United Nations Treaty Series
(UNTS) or any domestic treaty series. However, most of the important treaties referred to in this book
are available in a single collection.5 With court decisions, I have generally aimed at listing a material
source. With International Court of Justice (ICJ) decisions, this has been the ICJ Reports; with other
cases, this has often (if not invariably) been the invaluable International Law Reports or its
predecessor, the Annual Digest. Decisions of the European Court of Human Rights (ECtHR),
moreover, are far more easily accessible on the Court's website6 than in any published form.

Since this book is the product of more than twenty years of teaching, the number of people to
whom I have become indebted is way too large to be listed. Still, a few need to be singled out. The
late Bert Vierdag gave me my first official teaching job in 1990, at the University of Amsterdam.
Martti Koskenniemi brought me to Helsinki six years later, and has been and remains a close friend
and an immense influence. I have benefited from having some extremely good teachers, including
Gerd Junne, Pieter Jan Kuijper and Richard Lauwaars, and my approach to international law and the
global order reflects their influences. Not only did they teach me properly about international law and
international politics, they also taught by example about good teaching. And then there is the
influence of more than twenty generations of students, at Amsterdam, Helsinki and a variety of other
places.

Many colleagues suggested things to read; I owe all of them a big ‘thank you’. Antti Kivivuori
and Alice Neffe provided me with specific materials. I am heavily indebted to Magda Kmak and Rain
Liivoja, who read some of the draft chapters and provided useful comments, as did several anonymous
reviewers for Cambridge University Press. Working with the Press has been, as always, a delight,
thanks to the wonderful support offered by Finola O’Sullivan and Sinead Moloney. This book is
dedicated to my wife Margareta and my children, Johan and Gilda.

1 James Crawford, Brownlie's Principles of Public International Law, 8th edn (Oxford University
Press, 2012); Malcolm Evans (ed.), International Law, 3rd edn (Oxford University Press, 2010); and
Malcolm Shaw, International Law, 6th edn (Cambridge University Press, 2008).

2 See José E. Alvarez et al., ‘The Shape of Global Governance’ (2010) NYU Law School Magazine,
22–9, also available at http://blogs.law.nyu.edu/magazine/2010/roundtable-global-
governance/ (visited 25 May 2012).

3 See James Crawford and Martti Koskenniemi (eds.), The Cambridge Companion to International
Law (Cambridge University Press, 2012).

4 The best general overview available is Paul Craig and Gráinne de Búrca, EU Law: Text, Cases, and
Materials, 5th edn (Oxford University Press, 2011).

5 See Malcolm D. Evans (ed.), Blackstone's International Law Documents, 10th edn (Oxford
University Press, 2011).

6 At www.echr.coe.int/echr/.

List of abbreviations

BIT
Bilateral investment treaty

CAR
Comision Administradora del Rio Uruguay (Executive Commission on the River Uruguay)

CISG
Convention on Contracts for the International Sale of Goods

CITES
Convention on International Trade in Endangered Species of Wild Fauna and Flora

CJAC
Central American Court of Justice

CJEU
Court of Justice of the European Union

COP
conference of the parties

COPUOS
Committee on the Peaceful Uses of Outer Space

DSB
dispute settlement body (WTO)

DSU
dispute settlement understanding (WTO)

ECHR
European Convention on Human Rights

ECtHR
European Court of Human Rights

EEZ
exclusive economic zone

EFTA
European Free Trade Agreement

ENMOD
Environmental Modification Convention

ETS
European Treaty Series

EU
European Union

EULEX
European Union Rule of Law Mission in Kosovo

FATF
Financial Action Task Force

FRG
Federal Republic of Germany (former West Germany)

FSIA
Foreign Sovereign Immunities Act

GATS
General Agreement on Trade in Services

GATT
General Agreement on Tariffs and Trade

GDR
German Democratic Republic (former East Germany)

IATA
International Air Transport Association

ICAO
International Civil Aviation Organization

ICC
International Criminal Court

ICCPR
International Covenant on Civil and Political Rights

ICESCR
International Covenant on Economic, Social and Cultural Rights

ICISS
International Commission on Intervention and State Sovereignty

ICJ
International Court of Justice (World Court)

ICSID
International Centre for the Settlement of Investment Disputes

ICTR
International Criminal Tribunal for Rwanda

ICTY
International Criminal Tribunal for the former Yugoslavia

IDA
International Development Agency

IFC
International Finance Corporation

ILA
International Law Association

ILC
International Law Commission

ILO
International Labour Organization

IMCO
Intergovernmental Maritime Consultative Organization

IMF
International Monetary Fund

IMO
Intergovernmental Maritime Organization

IMT
International Military Tribunal (Nuremberg Tribunal)

INBAR
Organization for the Management of the Global Trade in Bamboo and Rattan Products

IOSCO
International Organization of Securities Commissions

ITC
International Tin Council

ITLOS
International Tribunal for the Law of the Sea

ITU
International Telecommunications Union

IWC
International Whaling Commission

MARPOL
International Convention for the Prevention of Pollution from Ships

MFN
most favoured nation

MIGA
Multilateral Investment Guarantee Agency

MOP
meeting of the parties

MoU
memorandum of understanding

NAFO
Northwest Atlantic Fisheries Organization

NATO
North Atlantic Treaty Organization

NGO
non-governmental organization

OECD
Organization for Economic Cooperation and Development

OSPAR
Convention for the Protection of the Marine Environment of the North-east Atlantic

PCA
Permanent Court of Arbitration

PCIJ
Permanent Court of International Justice

PISA
Programme on International Student Assessment

PLO
Palestine Liberation Organization

POP
persistent organic pollutant

R2P
responsibility to protect

SDR
special drawing right

SEC
US Securities Commission

SFRY
Socialist Federal Republic of Yugoslavia

SOLAS
International Convention for the Safety of Life at Sea

TFEU
Treaty on the Functioning of the European Union

TRIPs
trade-related aspects of intellectual property rights

UN
United Nations

UNCLOS
United Nations Conference on the Law of the Sea

UNCTAD
United Nations Conference on Trade and Development

UNEF
United Nations Emergency Force

UNEP
United Nations Environment Programme

UNESCO
United Nations Educational, Scientific and Cultural Organization

UNHRC
United Nations Human Rights Committee

UNITA
Uniao Nacional para a Independencia Total de Angola (Angolan rebel movement)

UNMIK
United Nations Mission in Kosovo

UNTAET
United Nations Administration in East Timor

UNTS
United Nations Treaty Series

VCLT
Vienna Convention on the Law of Treaties

VOC
Verenigde Oost-Indische Compagnie (United East India Company)

WHO
World Health Organization

WTO
World Trade Organization

Part I The structure of international law

1 The setting of international law

Introduction

As anyone who has ever bought a product from abroad should realize, the purchase is possible
because there are rules that make it so. As everyone who has ever hopped on an airplane abroad, or
sent a postcard abroad or watched a foreign television channel should realize, there are rules that
facilitate doing so. These rules form part of a broader network of rules usually referred to as
international law. International law is not just the law (if any) that deals with war and peace, or with
genocide and human rights; it also encompasses rules on trade, on protection of the environment, on
shipping and on the protection of refugees. Few of these rules are uncontroversial, and even fewer
work perfectly, but the bottom line should be clear: the existence of international relations, of
whatever kind, entails the existence of international law. As the ancient Romans knew, wherever
there is a society, there will be law (ubi societas, ibi jus), and the rules regulating contacts within the
society of states are generally called international law. It is these rules that form the topic of this book
or, more precisely, this book is dedicated to providing a framework for the further study of those rules
in detail, since there are far too many international legal rules to fit within the pages of a single
volume.

More specifically, this book is dedicated to the study of public international law, as opposed
to private international law. Whereas private international law regulates individual conduct with a
transboundary element (international contracts, international marriages or international traffic
accidents, for example), public international law is often said to regulate relations between states.
While saying so is still acceptable, it should be with the caveat that many of the rules of international
law have an effect not only on states, but also on other entities, be they companies, individuals or
minority groups. Likewise, many of the rules are shaped not just between states but also involve
representatives of international organizations (such as the UN), or civil society organizations (such
as Greenpeace).

Any international lawyer, whether she realizes it or not, works on the basis of a set of assumptions
about what the world is like and, more specifically, what international law is like. In other words, all
international lawyers utilize some kind of theory of international law. This can be a highly pragmatic
theory, something to the effect that international law exists to serve peaceful relations between states
and should be regarded from that perspective as a technical discipline, providing the tools for
statesmen. This, arguably, is the dominant approach among international lawyers. It can also be a
highly sophisticated and politically self-conscious theory, e.g. a theory holding that international law
is the handmaiden of global capitalism, therewith complicit in oppression, and thus to be regarded
with suspicion and a critical eye. It can be a theory viewing international law as a beacon of hope for
the poor and oppressed – such a theory often undergirds the activities of those who specialize in

human rights. And it can be a nationalist theory that starts with national self-interest, in which case
international law is often viewed as an intruder, aiming to undermine national decision-making
processes – such a view is not uncommon among social conservatives. Those who tend to view
international law as either a tool for statesmen or as a beacon of hope tend to have a cosmopolitan
outlook; they expect international law to be able to bring about a better world, and for them,
‘sovereignty’ is a four-letter word. By contrast, those who view international law as either intrusive
or as the handmaiden of global capitalism tend to be less cosmopolitan; to them, ‘sovereignty’ is
actually a useful shield.

Either way, whatever the lawyer does, whatever the lawyer writes and whatever the lawyer thinks,
will in some way be based on an underlying set of ideas and assumptions about what the function of
international law is, and what role it should play. International law, in other words, cannot be
portrayed as politically innocent. This makes it imperative that a book such as this one starts with an
overview of how international law has come about, what sort of role it has played and what sort of
role it could play.

The seventeenth century

By general acclamation, the history of modern international law (international law as we know it) is
usually said to have started in the seventeenth century. That is not to say that there were no
international rules before that date; the ancient Greek city states had already concluded treaties with
each other on such matters as how best to treat prisoners of war; the Roman Republic devised an
intricate system for dealing with foreign merchants; and during the middle ages, when the city states
of Italy were significant actors, the institutions of diplomacy developed, complete with embassies and
diplomats and guarantees that their activities would not easily be interfered with by their host states.1

Still, the seventeenth century stands out, for a variety of reasons. One of these is that for much of
the time preceding the seventeenth century, much of Europe tended to be organized in large empires,
from the Roman Empire to the reign of Charlemagne. And since Europe, in those days, was thought
to be congruent with the world at large, the result was that people did not think too much in terms of
there being different political entities requiring a specific legal system to organize their relations.
Instead, they tended to think of their empires as single entities, with the consequence that law was
largely conceptualized as internal.2

Possibly the most relevant reason why the seventeenth century stands out is that in the year 1648,
the Peace of Westphalia was concluded to mark the end of the Thirty Years' War. In Münster and
Osnabrück, two cities in today's Germany, the secular power of the pope, the leader of the Catholic
Church, came to a definitive end. It was agreed to confirm an earlier arrangement emanating from the
1555 Peace of Augsburg, to the effect that Europe would be divided into a number of territorial units,
and that each of these units could decide for itself which religion to adopt: cuius regio eius religio.
No outside interference was permitted, the result being the creation of sovereign states and, therewith,
the birth of the modern state system.3

It was perhaps no coincidence that it was precisely the state that came out of the middle ages as
the dominant form of political organization. Other entities (city states, feudal entities or a league of
trading posts such as the Hanseatic League) lost out, for unlike states, they lacked full territorial
control and, more important still, they lacked the capacity to guarantee commitments. What made the
state dominant was that it had the authority to live up to its commitments, precisely by controlling
territory.4

The second important event in the seventeenth century, as far as the development of international
law is concerned, was the publication in 1625 of Hugo Grotius’ On the Law of War and
Peace. Grotius had already been established, by then, as a leading intellectual,5 and he had been
influential (much to the benefit of the Dutch East India Company, the Dutch vehicle for colonial
exploitation) in shaping international law so as to uphold the freedom of the seas. This guaranteed
free shipping for the Dutch fleet, and made it impossible for other countries, such as Spain, Portugal
and England, to legitimately claim authority over the high seas. And this, in turn, proved highly
beneficial to Dutch trading interests. Indeed, as one commentator notes, among Grotius’ innovations
is his notion that all peoples have a right to trade; consequently, trading routes, such as the seas, ought
to be free as well.6 And all this, in turn, allowed Amsterdam to become the centre of global finance
and paved the way for the Dutch Golden Century.

It is sometimes suggested that Grotius is the founding father of international law, but such a claim
is untenable. For one thing, international law was not invented by a single person, but grew out of the
interactions of states and the commentaries of learned observers. Second, if there were a single
creator, then there are a few other serious contenders. Two of those are the Spanish theologians Suarez
and Vitoria, who preceded Grotius by a few decades. Vitoria in particular was highly instrumental in
devising the moral justification for the creation of a legal system that would facilitate the spread of
global capitalism.7 Likewise a serious contender for paternity, a little over a century after Grotius,
the Swiss Emeric de Vattel was the first (arguably) to have written a comprehensive manual on
international law, to be used by the chancelleries of the world.8

However, that is not to deny Grotius’ relevance. Grotius’ main claim to fame resides in two
circumstances. First, he forms a bridge between the classic naturalist way of looking at law and later
positivist theorizing. Natural law thinking typically suggests that law is not made but found; it exists
somehow in nature – it is often thought to be ordained by God – and can be recognized by the proper
method of analysis or by those of the right faith. Positivism, by contrast, wary of the subjectivity
inherent in such an approach, typically suggests that law is not given, but man made; law is whatever
states decide or agree it is. Grotius’ work encompassed elements of both viewpoints.

Second, Grotius may well have been the first to present a synthetic, comprehensive vision of
international law.9 On the Law of War and Peace addresses, as its title suggests, not only the law of
armed conflict and aggression, but also such matters as the binding force of treaties. That is not
necessarily to say, as is sometimes asserted, that Grotius developed the idea of an interconnected
international community with its own legal system; instead, more modestly, he may well have been
the first to lay down a specific set of binding international obligations, mostly inspired by the desire
to lay down the limits to proper statecraft.10

Colonialism

It is no exaggeration to state that international law has been closely connected with imperialism and
colonialism.11 The emergence of early modern international law is comprehensible in light of the
struggle between European powers for influence elsewhere in the world. It has already been
mentioned how Grotius contributed to the freedom of the seas, a freedom that stood his Dutch
employers in good stead, as freedom of the seas allowed freedom of discovery and freedom to trade.
These freedoms presupposed, however, that certain rules were considered to be in place in order to
regulate relations with ‘the natives’ in continents such as the Americas and Asia.

Among these rules was the rule that territories found overseas were to be regarded as not having
been subject to sovereignty – as territory belonging to no one (terra nullius). In other words,
stumbling on territory in Asia or the Americas, the European powers could proclaim that those
territories belonged to them; the original inhabitants were, by and large, ignored. This required quite
a balancing act, because these same original inhabitants were of the utmost importance when it came
to making trading deals; the peoples of the Americas and Asia were, after all, deemed capable of
concluding contracts with the Europeans, even contracts that would allow the Europeans exclusive
trading rights in valuable commodities such as pepper or nutmeg. Hence, an ambivalent picture
emerges. For purposes of establishing sovereignty, the local population was often ignored; but for
commercial purposes, their consent was deemed vital, at least as an argument to convince competing
European powers.

Much of the globe became the playground of the European powers, and at some point the non-
European world (the New World, in a highly eurocentric term) was literally divided between two of
them. In 1493, the pope issued a papal bull (Inter Caetera) drawing a line through the Atlantic Ocean.
Most of the territory to the west (with the exception of Brazil) was said to belong to Spain, while
Portugal claimed some of the territories to the east. This was confirmed a year later in the Treaty of
Tordesillas. With both countries further expanding east and west, they met again in the Pacific Ocean,
which resulted in the Treaty of Saragossa, concluded in 1529 and effectively sealing the division of
the world.12

Later, towards the end of the sixteenth century, England and Holland emerged as maritime
powers, breaking the trading monopolies of the Portuguese in the Indian Ocean and thus also bringing
the Spanish-Portuguese domination to an end. The Dutch, in 1602, created the Verenigde Oost-
Indische Compagnie (United East India Company, VOC in abbreviated form),13 and assigned it a
trading monopoly. One important ramification was that the VOC came to exercise delegated
governmental authority; it could acquire and administer territory, declare war and conclude treaties
and seize foreign ships. In 1603 this provoked an incident with Portugal, when the Dutch seized the
Portuguese vessel Santa Catharina. In order to legitimate this act, the VOC asked Grotius to write on
its behalf, which he duly did. In Mare Liberum, originally written as part of a larger work on prize
law (De jure praedae) but separately published in 1609, Grotius argued that the high seas were
not terra nullius (as the Spanish and Portuguese had implicitly presumed), but rather terra communis:
common property, and thus not susceptible to occupation and sovereignty.

This in turn led to English protests, as the English insisted on exclusive rights to the high seas
around the British isles, therewith effectively advocating the idea that states could generate maritime
zones. Negotiations between the English and the Dutch ensued (with Grotius a prominent member of
the Dutch delegation), but to little avail. It was only in the mid-seventeenth century that the Dutch
came to accept – without formally acknowledging as much – the British position: John Selden's Mare
clausum, presented in 1635, was finally grudgingly accepted. In fact, this signified that the British
had become too strong to resist and that the balance of power had shifted; Spain and Portugal no
longer reigned supreme, and Holland's position too was dwindling.

International law also played a marked role when it came to slavery, first by allowing it, and later,
in the course of the nineteenth century, by gradually arriving at a prohibition. The abolition, curiously
perhaps, was followed by the colonization of Africa. Whereas earlier Africa had been used as a vast
reservoir of slave labour but without being colonized, once slavery and the slave trade had been
legally abolished,14 the European powers saw fit to conquer the continent in what has become known
as the scramble for Africa.15 In particular the French and English sublimated their animosities by
occupying large tracts of land, with Germany, Portugal and Belgium playing smaller roles. This is
not to say that the latter were somehow less exploitative or more benign; in particular Belgium's reign

in Congo (or rather, King Leopold's personal reign in Congo) emptied the country of many of
its riches.

International law and the global economy

If colonialism was about trade and economic gain, which to some degree it was, this should already
be sufficient to suggest that to a large extent, international law is in one way or another connected to
the economy.16 Sometimes this is obvious: institutions such as the World Trade Organisation (WTO)
or the International Monetary Fund (IMF) have been explicitly established to regulate aspects of
economic life, and the various commodity arrangements so popular during the 1960s and 1970s to
regulate markets in products such as coffee or cocoa sprang from more or less the same impulse to
regulate economic life.

Less obviously perhaps, such phenomena as territorial rights or maritime demarcation owe much
to economic concerns as well. Grotius had already advocated free trading routes, not so much out of
a love of freedom (although that may have played a role as well), but also because free trade would
bring enormous economic benefits – at least for the Dutch.

For much of the second part of the twentieth century, the cases that would reach the ICJ tended
to be those involving the precise limits of territorial ownership, either on land or, more commonly, at
sea. And they often found their cause in the discovery of oil and natural gas deposits; whereas states
were not all that interested in establishing the precise boundaries of their jurisdictions earlier, they
became a lot keener when they realized that they might be sitting on huge oil reserves.

This also marks the impotence of international law though, at least on occasion; faced with the
possibility of economic profit, states have been less than fully obedient to the classic non-intervention
principle. As it could be economically beneficial to have friendly governments in place in states
boasting oil reserves, so Western states made sure to help put such friendly governments in place. In
what is a sad recurrence in twentieth-century history, the British and Americans have been
instrumental in toppling various Iranian regimes; the French have played a dismal role in western
Africa; and one might argue that the war between Iraq and Kuwait owed much to the UK again – the
original boundary treaty at issue had been concluded in the 1930s by the British (ruling Kuwait) with
themselves (effectively running Iraq as a mandate territory).

In short, much (though not all) of international law is related to the economy; international law
is, in part, the legal system regulating the global economy, in much the same way as it has been
observed that domestic legal systems and law school curricula (at least in the Western world) from
the late nineteenth century onwards were set up so as to facilitate the capitalist economy.

The rule of law, as the great German sociologist Max Weber observed, served to create legal and
economic certainty – its precise content was long considered less relevant.17 Giving effect to the idea
of the rule of law, central topics to be studied in law schools were contract, property, civil procedure,
torts and criminal law.18 Something similar applies to international law which, as T. E. Holland had
already noted in the late nineteenth century, was effectively private law applied to public actors.19 The
central topics in the international law emerging at the end of the nineteenth century included the law
of treaties (still often deemed to be contract law writ large), the law of responsibility (modelled on
tort law), acquisition of territory (the equivalent of property) and dispute settlement (which mimics
civil procedure). Only criminal law remained missing, a situation often ascribed to the circumstance
that international law does not emanate from a single sovereign authority. In a world of sovereign

equals without overarching authority, so the argument goes, it is difficult to think of criminal law to
begin with.

Over recent decades, however, international law has also come to embrace a version of criminal
law, albeit with a twist; in international criminal law, the central actors are not states, but
individuals.20 This helps to perpetuate the idea that the legal order remains based on sovereign states;
even though states cannot be imprisoned, there is no obstacle to sending individuals acting in the
name of the state to prison.

The international legal system

The absence of a single overarching authority is perhaps the most noteworthy characteristic of
international law. Indeed, for those who insist that law is only really law if and when it emanates from
a single sovereign, international law cannot really be law. At best, as the nineteenth-century positivist
thinker John Austin put it, international law can be seen as ‘positive morality’: it is more or less
binding on states, but as a matter of morality, not as a matter of law.21 While Austin's conclusion
followed from the way he defined law and not so much from anything inherent in international law
itself, and more recent theorists do not hesitate to refer to international law as ‘law’ proper, none the
less Austin's point has struck a chord. How, indeed, does international law function if it has no
sovereign authority? How are its rules made, in the absence of a legislator, and, perhaps even more
puzzlingly, how can the system work in the absence, by and large, of a police force, a Department of
Justice, a set of prosecutors and all the other characteristics we usually associate with legal systems?
That is a relevant question because, the occasional headline news notwithstanding, international law
seems to work reasonably well. Louis Henkin once put it memorably when he wrote that ‘almost all
nations observe almost all principles of international law and almost all of their obligations almost all
of the time’.22

Various explanations are offered for this state of affairs. One is that since states themselves make
international law, they have little incentive to break it; it makes little sense to create a rule on Monday,
only to ignore it on Tuesday or next Monday. Of course, circumstances may change, and if that
happens states may be tempted to breach their obligations, but in the normal course of events this is
not lightly to be presumed.

Related to this is the explanation of bureaucratic inertia. A civil servant who routinely implements
an international legal norm five days a week will not all of a sudden tell herself that she should stop
doing so. The implementation and application of law is very much a matter of habit and routine, and
this is no different in international law. In other words, unless something dramatic happens (a new
treaty, a new court ruling, a new government perhaps), states will continue to do what they are used
to doing and this typically helps strengthen international law. In addition, lawyers play a prominent
role at foreign ministries and other government departments; it has been suggested (but this may be
wishful thinking…) that their legal training instils in them a respect for the law and the professional
reflex to accept its authority.

An important role is also played in international law by considerations of reciprocity.23 If states A
and B are at war, and A starts to mistreat B's citizens by violating the Convention on Prisoners of
War, then B will be highly tempted to mistreat A's citizens as well, and may also start to violate that
convention. Much the same applies in other branches of the law: if X opens Y's diplomatic mail, Y
may do the same with X's diplomatic mail. Not all of international law rests on this specific form of
reciprocity, of course. It would be self-defeating to apply the same logic in cases of environmental

damage, for instance (‘If you pollute your rivers, then I shall pollute mine’) or in respect of human
rights (‘If you torture your citizens, I shall torture mine’),24 but that is not to deny that reciprocity can
act as a powerful force in international law.

A more recent explanation focuses on the role of legitimacy. A rule that is generally perceived as
useful and that has been created in the proper manner may be seen as legitimate and thereby exercise
a ‘compliance pull’. States need not be reminded that they need to adhere to such a rule; instead, they
would want to adhere to it – it would be the right thing to do.25

Other considerations which may help explain why international law is reasonably well complied
with include the idea that states are few in number and are attached to their territories; they cannot
escape from each other, and it is decidedly costly to be a pariah state. While bank robbers can flee
from the law by escaping to another country (preferably one without extradition agreements), states
have no such option. They have to interact with each other, and when doing so, it helps to have a
good reputation – no one wants to do business with a state that routinely violates its commitments. In
social science parlance, there is a social sanction in place, which helps to stimulate law-abiding
behaviour, as it is ultimately beneficial to be a member of the international community in good
standing.26

This final point already suggests that international law is not completely devoid of sanctions.
There is, admittedly, no international police force, and no international prison where states can be
locked up, but the social sanction of becoming a pariah state may be quite strong. In addition,
international law does have some mechanisms to deal with violations, even if not all of these can
properly be called ‘sanctions’, and here too reciprocity plays a prominent role.27

A practically relevant method of expressing dismay with another state's actions is the so-called
retorsion. These are measures taken within the limits of the law and send the message that a state is
not best pleased with another's actions. Typical examples would include recalling the ambassador
‘for consultation’,28 or the breaking off of diplomatic relations altogether. Such activities send strong
political messages, but do so without involving any breach of international obligations; the sanction
is, so to speak, purely political. This is not the case with what used to be called reprisals, nowadays
most often referred to by the more anodyne term ‘countermeasures’. These are characterized by their
own illegality, but this illegality is rendered lawful if they are done in response to an earlier wrongful
act committed by the other side.

An important related mechanism is well known from domestic contract law; if A violates a treaty,
then B may do the same, or inadimplenti non est adimplendum. The principle came before the
Permanent Court of International Justice (PCIJ) in 1937, in a case between Belgium and the
Netherlands concerning the regime relating to a river running through both countries. Belgium alleged
that the Netherlands had violated a treaty commitment, and while the Court's majority rejected this
claim, none the less Judge Anzilotti disagreed, and held in a dissenting opinion that Belgium would
in turn have been entitled to do the same. He found the principle of inadimplendi non est
adimplendum to be ‘so just, so equitable, so universally recognized, that it must be applied in
international relations also’.29

Other measures include self-defence and collective security action (including individual
sanctions); and since the 1990s international law has even been in a position, on occasion, to imprison
individuals who have committed war crimes and related acts; those convicted by the Yugoslavia and
Rwanda tribunals can testify to this, even though it took the International Criminal Court (ICC) (in
existence since 2002) a decade to decide its first substantive case. All this is better discussed
elsewhere in this book, but it goes to show that the popular notion that international law is a system
without sanctions is, at best, only partly true.

International legal theories

If Henkin was right when he suggested that states almost always adhered to almost all their
obligations, then the question of whether international law is actually ‘binding’ would hardly appear
relevant. What matters, one might say, is that international law seems to work; whether it does so
because it is somehow binding, or for some other reason, is practically of little relevance. Yet the
question has occupied international lawyers since times immemorial and quite obviously, when
judging a state's behaviour, it may matter whether the state was deemed to be bound by a rule of
international law, or whether it merely violated a rule of comity or some social practice. A refusal by
a state to put out the red carpet for a foreign head of state may violate a rule of etiquette, but is unlikely
to end up before any court, for the simple reason that there is no rule of international law which says
that one should welcome foreign heads of state with a red carpet.30

But even if it is accepted that international law is binding, the question arises of where that law
comes from. Earlier thinkers, before the Reformation and for quite some time thereafter, tended to
think that international law was natural law; it was given by God, and could be recognized by those
who adhered to the right religion. The problem with such a view turned out to be, eventually, that it
was inherently subjective. Those of a different faith might reach different conclusions, and even
people adhering to the same faith might come to different conclusions involving one and the same
incident.

Hence, by the nineteenth century, the tide had turned a little, and naturalism had by and large
been replaced by a more scientific-looking positivist approach, riding on the coat-tails of the emerging
social sciences.31 Positivism starts from the position that law does not hover about in nature but is,
instead, man made. In other words, the contents of law can be discovered by looking at what states
actually do. This looked very sensible for a while, until people started to realize that if the law is what
states do anyway, then it does not have much of a normative function.

The critical revolution in international law, spearheaded in the 1980s by David Kennedy
at Harvard and Martti Koskenniemi in Helsinki, has made it clear that international law is in actual
fact constantly in search of a compromise between the naturalist and the positivist traditions.32 As
Koskenniemi in particular has demonstrated, international law has to be both naturalist (in that it has
to serve the common good of mankind, in today's version – the direct link to God is thought to have
little credibility these days) and positivist (reflecting state practice and interests) at the same time.
This is now structurally impossible: international law is not capable of doing both at the same time.
As a result, whenever someone invokes a naturalist argument, it is vulnerable to a positivist critique
and vice versa.

By way of example, the naturalist may say that nuclear weapons are a terrible invention; the
positivist may reply that even so, there is no treaty outlawing them. Should the positivist draw the
conclusion that their use is therefore perfectly legal, the naturalist may respond that even though there
is no treaty prohibiting nuclear weapons, there is no clear rule allowing for their use either – at no
point has anyone actually been given permission to develop and use nuclear weapons. This discussion
can go on forever and is, indeed, bound to go on forever, unless and until states reach some kind of
agreement on what to do. Asking the ICJ for an opinion will prove useless in the absence of any clear
political accord: all the Court can do (and did in fact do, when asked, in 1996)33 is to declare either
that the use of nuclear weapons is generally illegal, but sometimes legal, or the other way around.
The trick then, of course, resides in finding out what the word ‘sometimes’ means. The consequence
of all this, in Koskenniemi's words, is that international law is eventually the continuation of politics.
It offers a framework and a vocabulary for the conduct of politics, but does not, and cannot, offer any
solutions, precisely because it has to appeal both to justice and to everyday practice at the same time:

‘Modern international law is an elaborate framework for deferring substantive resolution elsewhere:
into further procedure, interpretation, equity, context, and so on.’34

If international law is inherently political, it seems to follow that its political positions can be
elucidated. Some have studied how international law has been related to colonialism, or how it serves
the needs of a global market economy. In turn, this has spurred activities to explore and use
the emancipatory potential of international law more fully; after all, if international law is politics in
disguise, then it follows that it can also be utilized for worthy causes. Karen Knop, for example, has
studied how the right to self-determination has been used by disadvantaged groups in order to upgrade
their status;35 Hilary Charlesworth and Christine Chinkin have developed a feminist outlook on
international law;36 some scholars aim to develop a Marxist perspective on international law,37 and the
critical revolution has stimulated the emergence of scholars aiming to improve the plight of
developing nations.38 A useful side effect of all this is that few still believe in the fiction of a neutral,
politically innocent international law. Where the political preferences of earlier international legal
authors were hidden behind a vocabulary consisting either of impressive Latin phrases (jus
cogens, erga omnes) or a quasi-scientific jargon in the case of positivism, the political preferences of
such authors today are mostly out in the open.

Since international law can be seen to continue political debate, instead of settling it, what often
matters in addition to the precise rules and principles of international law are the identity and mindset
of the people taking decisions, and the conditions under which this political debate can take place.
This has generated an interest among international lawyers in political philosophy, in particular in
theories of deliberative democracy39 as well as the republican tradition, which is often traced back to
Machiavelli.40 Noteworthy is also that international lawyers have started to look for guidance to the
Aristotelian tradition of virtue ethics, a tradition where what matters is not only that rules exist, but
also the character traits of the individuals who apply those rules.41

International law in international relations theory

Whether one thinks international law is useful or not often depends on the view one has of
international politics generally.42 Self-proclaimed realists tend to view international law as largely
irrelevant. For them, the international system is characterized by a struggle for power between states,
and states will do anything to further their self-interest. From this perspective states will only respect
international law when it is in their self-interest to do so, and will disrespect it when it is not. Either
way, international law does not do much work; it either reflects state interests or it is violated.43

The liberal institutionalist approach to international affairs is not quite as ready to dismiss
international law. Adherents to this approach tend to think that international law can be of relevance,
at least if properly designed to take states’ lust for power into account. Starting from similar premises
to the die-hard realists (states are primarily motivated by self-interest), they have identified that
international law may be helpful in some walks of life, such as trade and investment, because legal
rules tend to create certainty and create stable expectations. Law may help reduce transaction costs
and for that reason alone it can be beneficial and serve a state's self-interest; while there may be costs
involved (sometimes having to accept a negative court decision, for example), the benefits may
outweigh them.44 Thus, a state that is a member of the WTO and regularly participates in trade
negotiations does not need to worry, if it wants market access elsewhere, about whom it should talk
to, what sort of access rules would be acceptable and even whether the other state will respect its
commitments. WTO membership makes all of these things easier and more predictable. Hence, in
certain circumstances, legal rules can have their advantages; the drawback, then, is that this helps to

instrumentalize law. If other, non-legal mechanisms could have similar advantages or even be more
beneficial for the user, then law would cease to play a role. It is no coincidence surely that one of the
leading representatives of this tradition, Robert O. Keohane, has in recent years started to extol the
virtues of legitimacy, not as an aspect of international law (as Franck, discussed in note 25, does), but
rather as its replacement.45

A variation on realism and in some hands, of liberal institutionalism, is the law and economics
approach, particularly prominent in US academia. This approach (‘law as economics’ as someone
once quipped) takes its cue not so much from political science but, as the label suggests, from
economics, in particular micro-economics. As economists tend to do when studying the behaviour of
firms or consumers, law and economics scholars typically presume that states are rational actors, and
presume that those rational actors act with profit maximization as their main goal. On these premises,
states will sometimes be inclined to adopt common rules, because common rules might lead to greater
profit maximization than going it alone. In other circumstances, the analysis suggests, unilateral
action may be preferable. In short, all the world's a market, to the law and economics scholars, and
while in good hands this approach is capable of generating illuminating insights,46 its underlying
premises need constantly to be interrogated. Is it really the case that states always act rationally?47 And
is it really the case that rationality goes hand in hand with profit maximization? And even if rationality
and thinking in economic terms applies to trade law or investment law, how can it explain the
worldwide prohibition of genocide or the near-universal acceptance of the Convention on the Rights
of the Child? Moreover, there is the risk that such an approach ends up denying, or even actively
undermining, the normative side of all things legal, because here in particular the risk of
instrumentalization looms large: if the law does not maximize profits, then perhaps some other route
ought to be chosen – perhaps even brute force.48

A final approach among international relations scholars is the so-called constructivist approach,
and this approach in particular takes international law very seriously.49 Where the realists and, to some
extent, the institutionalists tend to think of law as if all law were modelled on criminal law
(commands, backed by sanctions), constructivists are more inclined to view international law as
modelled on a private law conception; to their minds, international law is not just about prohibiting
things, but also about facilitating behaviour. International law allows states to conclude alliances, and
it helps channel political dialogue; it makes a lot of difference whether an incursion by one state into
a neighbouring state is discussed as an invasion, or as a humanitarian intervention or an exercise in
self-defence. International law, in short, delivers the framework and vocabulary that helps make
international politics possible. Without international law, there could not even be states, for how else
can such entities be classified as states except on the basis of rules that say so? Law, in other words,
helps to construct society, and is thus of immense importance.50 The relevant question is not the realist
question of whether law constrains, but rather whether it enables, social life.

Globalization, global governance and international Law

The emergence of globalization51 towards the end of the twentieth century has only strengthened the
connection between law and economics. While globalization is often considered to encompass more
than merely intensified economic relations (it is also often thought to include cultural, social and
environmental phenomena), none the less there is general agreement that economic globalization is a
key element in globalization, and that the existence of global economic relations demands a global
legal framework.

However, globalization affects more than the economy alone: it also affects cultural and social
relations, it has given religious sentiments a new boost, and because globalization is often considered
to make people feel insecure and alienated, it may also have sparked nationalist and regional feelings.
With globalization comes localization, with social disembeddedness comes a desire to feel embedded
again. We may all be watching Dancing with the Stars, but the stars have to be our local stars; it is
no fun for Finns to watch Japanese stars and no fun for the Japanese to watch Finnish stars.52

More than this, globalization has also come to be accompanied by what is sometimes referred to
as global governance: the exercise of authority, on the global level, outside regular legal
structures.53 This creates important challenges for international law. How should international lawyers
assess the financial rules created by, for example, the Basel Committee, or accountancy rules
developed by international accountancy boards? These are not easy to squeeze into the framework of
traditional international law, yet they have a profound effect on the everyday lives of millions of
people. Hence, globalization and global governance pose challenges not just by throwing up new
fields for regulation, but also, more fundamentally, by forcing international lawyers to rethink the
tools of their trade. Globalization and global governance make clear that many of the classic concepts
and categories of international law (even concepts as fundamental as ‘statehood’ or ‘treaty’) have
become outdated. Indeed, if international law wants to continue to have something meaningful to say
about the conduct of international politics, it will need to adapt itself to the changing world.

To some extent, that process is going on as we speak. For the last two decades or so international
lawyers have come to embrace an emerging international criminal law, aiming to curb the worst
excesses of political crime worldwide, which is intimately related to global governance. Others have
started to suggest that topics traditionally not considered to be part of international law should be
given fresh consideration; perhaps international taxation is better seen as part of the international law
of global governance than, as it stands, as the sovereign prerogative of states. Likewise, migration
has become such a widespread phenomenon, and a phenomenon of such great economic importance
in view of the remittances sent home by migrants, that international law can ill afford to leave the
regulation of migration to domestic legal orders. After all, a legal order which allows capital, goods
and services to move freely across frontiers should perhaps also think about the movement of people,
and not leave this to individual states. This might also help to propel labour law from its marginal
position on the fringes of international law; even though the International Labour Organization (ILO)
has existed since 1919, labour law is not something international lawyers regularly occupy
themselves with.54

Ethics and international law

It is sometimes claimed that international law is not very ethical, but that is a debatable claim. Before
the rise of the Westphalian system, the ethical contents of international law were not considered
problematic. If international law was God given, then by definition it would be ethical enough, and
such debates as did take place largely involved the vexed question as to whether war was always
wrong, or whether there were circumstances in which war, however nefarious, could none the less be
considered just.55

Perhaps the main problem nowadays is not so much that international law and ethics have nothing
to do with each other, but that different conceptions of the ethics of international law compete with
each other. Thus, some reacted furiously when the ECtHR decided, in 2007, that it could not decide
on a claim made by Kosovo citizens concerning the conduct of United Nations (UN) and NATO
troops in Kosovo; the Court found that since the acts complained of were ultimately attributable to

the UN, and since the UN was not a party to the European Convention on Human Rights, the Court
therefore had no jurisdiction over those acts. Hence, so the ethical argument goes, human rights were
sacrificed. Yet the contrary finding would also have run into ethical problems; it would have
amounted to punishing some of the UN's member states for activities of the UN itself, and that in
itself might also be construed as unfair.56

Likewise, while one can interpret the Arrest Warrant case of the ICJ as a defeat for human rights
(the Court held that a Congolese government minister was immune from prosecution despite his
possible involvement in human rights violations),57 one can also interpret it as a vindication for
deliberative politics. Rules on immunity make it impossible to harass government members, thereby
allowing international communication to take place without disturbance. And that too has an ethical
quality in and of itself.

That said, the claim that global ethics has remained underdeveloped is fair enough.58 Partly this
results from the circumstance that moral philosophers tend to think about the ethical duties of
individuals rather than of collectivities such as states. Indeed, it is contested whether collective actors
have the capacity to act ethically to begin with, at least if by this is understood the capacity to be
motivated by ethical reasons. One may say of an individual that she behaves charitably, but this is a
more difficult judgement when collective actors are involved.59

Moreover, it is often posited that individuals have stronger obligations towards people close to
them (family members, compatriots) than towards people elsewhere. As a result, much political ethics
focuses on the duties of individuals within a delimited community, such as a village or a state.
However, this type of work has led to important insights, which at least ought to inform international
law, such as the insight that global poverty is ethically unacceptable.60 Some moral philosophers have
started to analyse and discuss global ethics,61 and international lawyers themselves have tried to find
ways to express the fact that such activities as genocide, slavery and torture are ethically wrong, and
have come to use particular Latin phrases to express this sentiment (jus cogens), or even to hope that
if international law can be seen as constitutionalizing it will automatically follow that such activities
are prohibited.62

In short, it is not so much the case that international law is devoid of ethics, but rather that ethics
itself is far from uniform: different ethicists follow different traditions and present different
conclusions as to what exactly constitutes proper ethical behaviour, or whose behaviour counts,
ethically speaking.

Final remarks: a critical perspective

The idea behind this book is to introduce, albeit in a nutshell, the entire corpus of international law,
and to do so from a more or less critical angle. Among the main values of the critical approach is its
methodology; it makes clear that international law always has to navigate between naturalism and
positivism. Thus, the critical school has presented a useful tool for the explanation of international
law – many of the uncertainties of international law can be traced back to the tension between
naturalism and positivism, or between the community interest and the individual state interest, in
more modern language.

One ramification is that, throughout this book, I will usually refrain from comments about whether
the behaviour of states is lawful or unlawful. One of the fundamental teachings of the critical school
is that legal rules tend to have uncertain content precisely because they need to navigate between

positivist and naturalist positions (thus, they are ‘indeterminate’, in jargon) and, as a consequence, it

is often impossible to identify a single right answer to any legal question. Instead, the more proper

question to ask is whether behaviour can be legally justified; if state A sends its troops into

neighbouring state B, it should be able to justify this in legal terms, and if the justification is strong
enough, the behaviour can be deemed ‘lawful’. Often enough, this judgment (whether in the hands of

a court, other international lawyers,63 or of the public at large) will take place on a sliding scale:

behaviour is more or less justifiable in legal terms. Once a crucial point is passed (when the

justification is not strong enough) the behaviour may be deemed unlawful.

By the same token, it is useful to remember that rules typically come with exceptions, and it takes

a person or group of persons (such as a court) to decide whether to apply the rule or the exception;

none of this takes place automatically. Likewise, rules tend to be both over-inclusive and under-

inclusive: they will always cover events their drafters never thought of, and somehow manage not to

cover some of the events that they were intended to apply to.64 Hence, at the end of the day,

international law is not carved in stone, but the product of a practice of argumentation, in which the

individual characteristics of those evaluating the arguments, be they Foreign Office lawyers or judges,

plays an important role.65 With this in mind, it is time to start to discuss the structure, process and

contents of international law.

1 See G. R. Berridge, Diplomacy: Theory and Practice (London: Prentice Hall, 1995).
2 For an argument to this effect (albeit much more subtle), see J. M. A. Lenssen, ‘Vroeg-Middeleeuws
volkenrecht: Van Romeins Rijk tot Investituurstrijd’, in A. C. G. M. Eyffinger (ed.), Compendium
Volkenrechtsgeschiedenis (Deventer: Kluwer, 1989), 10–36.
3 The connections between the Peace of Augsburg and the Peace of Westphalia are emphasized in C.
G. Roelofsen, ‘De periode 1450–1713’, in Eyffinger, Compendium, 56–125, at 89–90.
4 The point is well made in Hendrik Spruyt, The Sovereign State and Its Competitors (Princeton

University Press, 1994). See also Chapter 4 below.
5 A fine biography in Dutch is Henk Nellen, Hugo de Groot: Een leven in strijd om de vrede 1583–

1645 (Amsterdam: Balans, 2007).
6 See Timothy Brook, Vermeer's Hat (London: Profile, 2008), at 67–8.
7 See Martti Koskenniemi, ‘Empire and International Law: The Real Spanish Contribution’
(2011) 61 University of Toronto Law Journal, 1–36.
8 As asserted by Marie-Hélène Renaut, Histoire du droit international public (Paris: Ellipses, 2007),

at 114. Dutch legal historian Roelofsen, however, while decidedly not a Grotian apologist, feels that
Grotius’ On the Law of War and Peace constitutes the first manual. See Roelofsen, ‘De periode 1450–
1713,’ at 109.
9 See Cornelis van Vollenhoven, De drie treden van het volkenrecht (The Hague: Martinus Nijhoff,

1918).
10 See Martti Koskenniemi, ‘International Law and raison d’état: Rethinking the Prehistory of
International Law’, in Benedict Kingsbury and Benjamin Straumann (eds.), The Roman Foundations

of the Law of Nations: Alberico Gentili and the Justice of Empire (Oxford University Press, 2010),
297–339.
11 Recent studies exploring the colonialist legacy of international law include
Martti Koskenniemi, The Gentle Civilizer of Nations: The Rise and Fall of International Law 1870–

1960 (Cambridge University Press, 2001), and Antony Anghie, Imperialism, Sovereignty and the

Making of International Law (Cambridge University Press, 2004).
12 See Roelofsen, ‘De periode 1450–1713’, at 69.
13 The English, incidentally, also had an East India Company, though this was less generously

endowed with delegated state powers.
14 Slave trade still exists (despite its legal prohibition), and is currently often referred to as human

trafficking.

15 For a fine study in Dutch see H. L. Wesseling, Verdeel en heers: De deling van Afrika 1880–
1914 (Amsterdam: Bert Bakker, 1991).
16 See generally also Claire Cutler, Private Power and Global Authority: Transnational Merchant
Law in the Global Political Economy (Cambridge University Press, 2003).
17 See Max Weber, Economy and Society: An Outline of Interpretive Sociology (Berkeley, CA:
University of California Press, 1978, G. Roth and C. Wittich eds.).
18 See Duncan Kennedy, ‘Legal Education and the Reproduction of Hierarchy’ (1982) 32 Journal of
Legal Education, 591–615 at 597.
19 See T. E. Holland, The Elements of Jurisprudence, 13th edn (Oxford: Clarendon Press, 1924), at
393–4.
20 See Chapter 12 below.
21 See John Austin, The Province of Jurisprudence Determined (Cambridge University Press, 1995,
W. Rumble ed., first published 1832), e.g. at 124.
22 See Louis Henkin, How Nations Behave: Law and Foreign Policy, 2nd edn (New York: Columbia
University Press, 1979), at 47 (emphasis omitted).
23 The seminal article is Stanley Hoffmann, ‘International Law and International Systems’, in Klaus
Knorr and Sydney Verba (eds.), The International System: Theoretical Essays (Princeton University
Press, 1961), 205–37.
24 The political scientist Robert Keohane helpfully distinguishes between specific and diffuse
reciprocity: the latter would apply to common interests. See Robert O. Keohane, ‘Reciprocity in
International Relations’, reproduced in his International Institutions and State Power: Essays in
International Relations Theory (Boulder, CO: Westview Press, 1989), 132–57.
25 See generally, and in considerably more detail, Thomas M. Franck, The Power of Legitimacy
among Nations (Oxford University Press, 1990). Franck similarly posited that a perception of the
fairness of a rule may inspire law-abiding behaviour. See Thomas M. Franck, Fairness in
International Law and Institutions (Oxford: Clarendon Press, 1995).
26 See Abraham Chayes and Antonia Handler Chayes, The New Sovereignty: Compliance with
International Regulatory Agreements (Cambridge, MA: Harvard University Press, 1995).
27 This will be further discussed in Chapter 9 below.
28 Thus, in April 2012, the Netherlands recalled its ambassador to Surinam (a former Dutch colony)
after Surinam had adopted legislation providing an amnesty to individuals associated with gross
human rights violations committed in the early 1980s.
29 See Diversion of Water from the Meuse, [1937] Publ. PCIJ, Series A/B, no. 70, at 50.
30 This is not to say they can be arrested at will; they will typically be immune from arrest, as will be
discussed in Chapter 5 below.
31 See Mónica García-Salmones Rovira, A Science of Interests: The Project of 20th Century Positivist
International Law (Ph.D. thesis, University of Helsinki, 2012).

32 See in particular David Kennedy, International Legal Structures (Baden-Baden: Nomos, 1987),
and Martti Koskenniemi, From Apology to Utopia: The Structure of International Legal
Argument(Helsinki: Finnish Lawyers’ Publishing Company, 1989). Koskenniemi's work was
reissued in 2005 by Cambridge University Press, with a new epilogue.
33 See Legality of the Threat or Use of Nuclear Weapons, advisory opinion, [1996] ICJ Reports, 226.
34 See Martti Koskenniemi, ‘The Politics of International Law’ (1990) 1 European Journal of
International Law, 4–32, at 28.
35 See Karen Knop, Diversity and Self-determination in International Law (Cambridge University
Press, 2002).
36 See Hilary Charlesworth and Christine Chinkin, The Boundaries of International Law: A Feminist
Analysis (Manchester University Press, 2000).

37 See e.g. Susan Marks (ed.), International Law on the Left: Re-examining Marxist

Legacies (Cambridge University Press, 2008).
38 This is known as the TWAIL movement, with TWAIL standing for Third World Approaches to

International Law. See e.g. Balakrishnan Rajagopal, International Law from Below: Development,

Social Movements and Third World Resistance (Cambridge University Press, 2003).
39 See e.g. John Dryzek, Deliberative Global Politics: Discourse and Democracy in a Divided

World (Cambridge: Polity, 2006).
40 See e.g. Samantha Besson and José Luis Martí (eds.), Legal Republicanism: National and

International Perspectives (Oxford University Press, 2009). See also M. N. S. Sellers, Republican

Principles in International Law: The Fundamental Requirements of a Just World Order (New York:

Palgrave MacMillan, 2006).
41 See e.g. Jan Klabbers, ‘Autonomy, Constitutionalism and Virtue in International Institutional
Law’, in Richard Collins and Nigel D. White (eds.), International Organizations and the Idea of
Autonomy(London: Routledge, 2011), 120–40. I will return to this in Chapter 17 below.
42 For a useful general overview, see Michael Byers, ‘International Law’, in Christian Reus-Smit and

Duncan Snidal (eds.), The Oxford Handbook of International Relations (Oxford University Press,
2008), 612–31.
43 The classic statement is Kenneth Waltz, Theory of International Politics (New York: McGraw-

Hill, 1979), in which international law hardly warrants a footnote. The sentiment is sometimes echoed

from within the legal community, where a rational choice perspective on international law ends up

dismissing its value. Recent examples include Jack L. Goldsmith and Eric O. Posner, The Limits of

International Law (Oxford University Press, 2005) and, far more sophisticated, Andrew

T. Guzman, How International Law Works: A Rational Choice Theory (Oxford University Press,

2008).
44 Some of the classic texts in this tradition include Stephen D. Krasner (ed.), International

Regimes (Ithaca, NY: Cornell University Press, 1983) and Robert O. Keohane, After Hegemony:

Cooperation and Discord in the World Political Economy (Princeton University Press, 1984).
45 See e.g. Allen Buchanan and Robert O. Keohane, ‘The Legitimacy of Global Governance
Institutions’ (2006) 20 Ethics and International Affairs, 405–37.
46 Some of the best work in this tradition is done by Trachtman. See e.g. Joel P. Trachtman, The

Economic Structure of International Law (Cambridge, MA: Harvard University Press, 2008).
47 The German-born political theorist Hannah Arendt observed, by contrast, that the field of

international relations was precisely the one field where reduction to economic factors would be

senseless, because the animosities and friendships between states are often inspired by other motives
(such as religion, ethnicity or history). See Hannah Arendt, ‘What is Freedom?’, reproduced in
Hannah Arendt, Between Past and Future (London: Penguin, 1968), 143–71.
48 And then there is, obviously, the distributive question: whose profit is being maximized?
49 Leading works in this tradition include Friedrich V. Kratochwil, Rules, Norms, and Decisions: On

the Conditions of Practical and Legal Reasoning in International Relations and Domestic

Affairs(Cambridge University Press, 1989), and Nicholas G. Onuf, World of Our Making: Rules and

Rule in Social Theory and International Relations (Columbia, SC: University of South Carolina

Press, 1989). A recent account combining constructivist thought with legal theory is

Jutta Brunnée and Stephen J. Toope, Legitimacy and Legality in International Law: An Interactional

Account (Cambridge University Press, 2010).
50 See generally also Andrew Hurrell, On Global Order: Power, Values, and the Constitution of

International Society (Oxford University Press, 2007).
51 Useful introductions include Thomas Hylland Eriksen, Globalization: The Key Concepts (Oxford:

Berg, 2007) and, highly readable, Alex MacGillivray, A Brief History of Globalization (London:

Robinson, 2006). A rare study about the challenges globalization entails for international law is David

J. Bederman, International Law and Globalization (New York: Palgrave MacMillan, 2008).
52 See generally Saskia Sassen, A Sociology of Globalization (New York: Norton, 2007).

53 Among the first to observe this were James N. Rosenau and Ernst-
Otto Czempiel (eds.), Governance without Government: Order and Change in World
Politics (Cambridge University Press, 1992), whereas a useful (political) framework is developed in
Deborah D. Avant, Martha Finnemore and Susan K. Sell (eds.), Who Governs the
Globe? (Cambridge University Press, 2010).
54 See also Jan Klabbers, ‘The Idea(s) of International Law’, in A. S. Muller et al. (eds.), The Law of
the Future and the Future of Law (Oslo: TOAEP, 2011), 69–80.
55 The classic study is Michael Walzer, Just and Unjust Wars, 3rd edn (New York: Basic Books,
2000).
56 See joined cases Behrami and Behrami v. France (Application no. 71412/01),
and Saramati v. France and others (Application no. 78166/01), decision of 2 May 2007, reproduced
in 133 International Law Reports, 1.
57 See case concerning the Arrest Warrant of 11 April 2000 (Democratic Republic of
Congo v. Belgium), [2002] ICJ Reports 3; this will be further discussed in Chapter 5 below.
58 See also Stanley Hoffmann, Duties beyond Borders: On the Limits and Possibilities of Ethical
International Politics (Syracuse University Press, 1981).
59 For a useful set of papers exploring the moral agency of collective actors, see
Toni Erskine (ed.), Can Institutions have Responsibilities? Collective Moral Agency and
International Relations (New York: Palgrave MacMillan, 2003).
60 See e.g. Thomas Pogge, ‘Divided against Itself: Aspiration and Reality of International Law’, in
James Crawford and Martti Koskenniemi (eds.), The Cambridge Companion to International
Law(Cambridge University Press, 2012), 373–97.
61 See e.g. Charles S. Beitz, Political Theory and International Relations (Princeton University Press,
1999 [1979]); Simon Caney, Justice Beyond Borders: A Global Political Theory (Oxford University
Press, 2005); Peter Singer, One World: The Ethics of Globalization, 2nd edn (New Haven, CT: Yale
University Press, 2004).
62 For a discussion of the latter, see Jan Klabbers, Anne Peters and Geir Ulfstein, The
Constitutionalization of International Law (Oxford University Press, 2009), and
Nico Krisch, Beyond Constitutionalism: The Pluralist Structure of Postnational Law (Oxford
University Press, 2010).
63 Schachter famously invoked an ‘invisible college of international lawyers’: if most international
lawyers find behaviour unlawful, then it probably is. See Oscar Schachter, ‘The Invisible College of
International Lawyers’ (1977) 72 Northwestern University Law Review, 217–26.
64 The idea that rules are both over-inclusive and under-inclusive is authoritatively formulated in
Frederick Schauer, Playing by the Rules: A Philosophical Examination of Rule-based Decision-
making in Law and in Life (Oxford: Clarendon Press, 1991).
65 See already Hersch Lauterpacht, The Function of Law in the International Community (Oxford
University Press, 2011 [1933]), at 111.

2 The making of international law

Introduction

International law, so many claim, is predominantly made by states, and this still holds true in large
measure. Since states are considered to be sovereign, it follows that there is no authority above them;
and if there is no authority above them, it follows that law can only be made with their consent –
otherwise the system would be authoritarian. Hence, international law is often said to be a consent-
based (or consensual) system.

International law does not have a specific document specifying how it is made; there is no treaty
on the correct ways and processes for making international law. Instead, the Statute of the ICJ contains
a listing of instruments that the Court may apply in deciding cases, and it is this listing that is often
used as a starting point for a discussion of the sources of the law. This already suggests that the list is
not exhaustive; it is possible that there are sources of law not mentioned in article 38 Statute ICJ. And
indeed, recalling that the same list already graced the Statute of the PCIJ and was drafted in the early
1920s, it seems eminently plausible that in the years since then, the possibilities for law-making have
expanded. It is plausible to say that international organizations can make law, although one can also
explain their resolutions as being treaty based, since the authority of such resolutions derives from
the constitutive instrument of the organization. There is widespread discussion (if little truly
conclusive) about the role of civil society and non-governmental organizations (NGOs) in the making
of international law. And there are heated debates about whether states can make so-called ‘soft law’,
and whether law can (and should be allowed to) arise through networks of civil servants and
regulators.

In this chapter and the next the sources of international law will be discussed. The current chapter
will concentrate on customary international law and general principles of law as well as sources
doctrine generally, whereas the next chapter will be devoted to the law of treaties. Before continuing,
however, it is imperative to first sketch the basics of the system, and underline the role of consent.
For while it may be the case that consent is of less importance nowadays than a century ago, it needs
to be underlined that state consent is still of vital importance.

Two ships (or perhaps three): Lotus and Wimbledon

On the second day of August 1926, the steamships Boz-Kourt (flying the Turkish flag)
and Lotus (French) collided on the high seas, off the Turkish coast. The Boz-Kourt was cut in two,
eight Turkish nationals died and the Turkish authorities started criminal proceedings against
Lieutenant Demons, first officer of the Lotus, as well as the captain of the Boz-Kourt, Hassan Bey.
Both were found guilty by the Criminal Court of Istanbul and sentenced to a fine and some months’
imprisonment.1

The fact that a French citizen (Demons) was being prosecuted in Turkey did not go down well
with the French authorities, who claimed that Turkey lacked the required jurisdiction to prosecute a
foreigner for acts committed outside Turkish territory. Turkey and France agreed to take the matter
to the PCIJ which in 1927 rendered its classic decision.2

The main question asked of the Court, as formulated by both parties together, was whether
Turkey, in instituting proceedings against Lieutenant Demons, had acted in conflict with principles
of international law. In other words, the question was not whether Turkey had permission to start
proceedings, but rather whether starting proceedings was prohibited. The Court actually agreed that

this was the proper way to ask the question, for it was ‘dictated by the very nature and existing
conditions of international law’.3

The Court discussed the nature of international law as follows, in a famous paragraph:

International law governs relations between independent States. The rules of law binding upon States
therefore emanate from their own free will as expressed in conventions or by usages generally
accepted as expressing principles of law and established to regulate the relations between these co-
existing independent communities or with a view to the achievement of common aims. Restrictions
upon the independence of States cannot therefore be presumed.4

Since no prohibition could be found in international law, the Court eventually decided that Turkey
had not violated international law. There was simply no rule prohibiting Turkey from starting
proceedings against Lieutenant Demons, in the circumstances of the case, and thus Turkey had done
nothing wrong.

This proved to be a monumental decision, as much for its reasoning as for its outcome. The Court
here laid down the idea of international law as a permissive system; behaviour must be considered
permitted unless and until it is prohibited. The alternative, as argued by France, would have been to
regard international law as a prohibitive system, where behaviour is only lawful if there is a rule that
specifically allows it. Then again, it is easy to exaggerate the monumentality of the Lotus case. In
most domestic societies, the same basic starting point applies; people can do as they please unless the
law says they can't. We do not normally need specific rules telling us that we are allowed to walk on
the sidewalk; instead, we are free to do so, unless there is a rule that prohibits walking on the sidewalk.
As one of the basic principles of the modern Rechtsstaat puts it, nulla crimen sine lege (no crime
without a law).

The Lotus case still echoes in international law. The Court's starting point (that states are
permitted to do whatever they please unless it is prohibited) is still valid enough, although it is
possible to claim that there are exceptions; surely committing genocide is wrong, even for those states
that have never accepted the prohibition of genocide.5 Some aspects of the decision
were questionable. Thus, the Court equated a Turkish ship with Turkish territory in order to establish
a jurisdictional link, even though strictly speaking the territory on which the collision occurred was
the high seas,6 and arguably it concluded too rapidly that in cases of collision the affected state could
exercise jurisdiction. Later treaties on the law of the sea limit the penal jurisdiction of states to the
flag state or the state of nationality of the responsible officer, which suggests some dissatisfaction
with the Court's broad jurisdictional sweep in the Lotus case.7

The Lotus case was decided by the casting vote of the Court's president, the Swiss lawyer Max
Huber, known for his ‘sociological jurisprudence’ and generally positivist outlook.8 Either way, the
decision should not have come as a surprise; four years earlier, in its first ever contentious decision
(the Wimbledon case), the PCIJ had strongly suggested the outlines of a positivist, permissive
international legal order.

After World War I the victorious powers negotiated the Versailles Treaty and then told Germany
to consent to it. Under the treaty, the Kiel Canal, in northern Germany, was declared an international
waterway; Germany could not block the passage of any ship, save in times of war. When Germany
refused access, in 1921, to the steamer Wimbledon, flying the English flag and chartered by a French
company, some of those victorious powers started proceedings in the PCIJ.9 France, the UK, Italy and
Japan, joined by Poland, claimed that in refusing access to the SS Wimbledon, Germany had violated
article 380 of the Versailles Treaty. One of Germany's counter-arguments, no doubt inspired by the
awkward circumstance that Germany had not been allowed to participate in the drafting of the

Versailles Treaty, was that the Versailles Treaty was difficult to reconcile with sovereignty. Surely
concluding a treaty could not be equated with giving up sovereignty, yet this, Germany argued, was
precisely what the internationalization of the Kiel Canal signified. Germany's argument invoked a
powerful theoretical point. How is it even possible to have law in a system of sovereign states?

The Court effectively shot down Germany's argument. While it agreed that concluding a treaty
could place restrictions on the exercise of sovereign rights, it disagreed with the position that
sovereignty and international law were fundamentally irreconcilable, and instead suggested that
sovereignty and international law went hand in hand: ‘the right of entering into international
engagements is an attribute of State sovereignty’.10

The two cases, Lotus and Wimbledon, together establish that in a horizontal order of sovereign
equals international law is by no means impossible; indeed, it is precisely because states are sovereign
that they can make international law. But the same sovereignty entails that rules can only be made on
the basis of consent; the rules of international law emanate from the freely expressed will of sovereign
states.

In other words, international law is often deemed a positivist system in that rules are created by
consent of the states themselves, and do not flow from elsewhere. International law does not stem
from religion (although historically this was often posited), or from considerations of morality, but
instead stems from the acts of the system's subjects. That is not to say that ‘natural law’ has no place
whatsoever; it is sometimes claimed that some rules are so important that they also exist without
consensual foundations, and may even bind those states that have not accepted them. Such rules are
known as jus cogensrules: peremptory rules from which no derogation is permitted, and examples
often mentioned include the prohibitions of genocide, torture, slavery and aggression.11

Article 38 Statute ICJ

After World War II the PCIJ was replaced by the ICJ. Drafted to become part of the Statute of the
PCIJ, in 1920, article 38(1) ICJ provides as follows:

The Court, whose function is to decide in accordance with international law such disputes as are
submitted to it, shall apply:

a. international conventions, whether general or particular, establishing rules expressly recognized by the
contesting states;

b. international custom, as evidence of a general practice accepted as law;
c. the general principles of law recognized by civilized nations;
d. subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified

publicists of the various nations, as subsidiary means for the determination of rules of law.12

It is generally agreed that article 38 does not establish a rigid hierarchy of sources, in particular when
it comes to the relationship between customary law and treaties; these can supersede each other and
also, as the Court confirmed in 1986, exist alongside each other.13 That said, two elements of
hierarchy can be seen in article 38. First, judicial decisions and the writings of the most highly
qualified publicists are listed as subsidiary means only, and the reference to article 59 ICJ Statute
further makes clear that judicial decisions have no precedent effect in international law; decisions of
the Court can only bind the parties to the dispute. This makes sense, of course; it follows from the
organizing principle of sovereignty that the Court cannot make law, but only apply it. Difficult as it

may be to draw the line between applying the law and making law, what is clear none the less is that
precedential effect would by definition involve law-making, and can thus not be accepted.

Second, there is also general agreement between international lawyers that general principles of
law (mentioned in subparagraph (c)) have as their main function the filling of gaps. In other words,
general principles will normally only be resorted to if there is a situation where there is neither an
applicable treaty nor an applicable rule of customary international law. Thus put, it would seem that
treaties and custom are the stronger sources, and that should perhaps not come as a surprise, as both
rest (at least in theory) firmly on the consent of states.

Treaties

Lord McNair, in his day the world's leading authority on the law of treaties, once described treaties
as the only, and sadly overworked workhorses of the international legal order.14 If states want to make
a deal (say, exchange territory), the only instrument at their disposal is the treaty. Likewise, they can
effectively only use the treaty form if the ambition is legislative in nature (e.g. to protect against
climate change or to guarantee human rights). The only instrument available to set up an institution
such as the UN is, again, the treaty. Hence, a lot is demanded from treaties and, especially during the
twentieth century, the treaty has become the dominant source of international law – or, if not of
‘law’ per se, then at least of rights and obligations.15

Accordingly, treaties can come in all forms and sizes. They can be bilateral but also multilateral;
they can be highly solemn and cast in language with biblical overtones (think of the designation
‘Covenant,’ which graced the constituting instrument of the League of Nations and is nowadays
associated with two general and universal human rights instruments), but also highly informal.
Typically, what matters is that states express their consent to be bound; in this way, being bound by
treaty can be reconciled with the starting point of state sovereignty.

Treaties have been concluded and have operated since time (almost) immemorial, and it stands to
reason that over the centuries, rules have developed, in customary international law, on the conclusion
of treaties, the effects and application of treaties, their validity and on their termination. These rules
have been codified in the 1969 Vienna Convention on the Law of Treaties (VCLT), which applies to
treaties concluded between states only. A later Vienna Convention was concluded (in 1986) to address
treaties concluded with or between international organizations, but this has yet to enter into force. In
the meantime, though, it is fair to say that treaties concluded with or between international
organizations are governed, by and large, by the same customary rules underlying the 1969 Vienna
Convention, and much the same applies to treaties involving yet other actors. Thus, a peace agreement
following a civil war, if governed by international law (as is normally the case), or an agreement
between a state and a mineral extraction company,16 will typically be subjected to the customary law
of treaties, and this, it is often claimed, is well-nigh identical to the 1969 Vienna Convention. These
rules will be discussed in greater detail in the next chapter, as will the question of what exactly
constitutes a treaty.

Customary law

People living in groups engage in all sorts of practices, and it is probably the case that all societies
recognize that in certain circumstances, those practices can acquire the force of law.17 This makes
some practical sense; it may be easier to regard activities that people do anyway as law, instead of
making written laws. While written law tends to be more precise, customary law has the advantage
that precisely because it is based on social practices, it is usually deeply engrained in the everyday
life of that society. In international law, characterized by the absence of a central legislator, customary
law has traditionally played a very important role, and continues to do so. When treaties were still
rare events, much of the law was based on the customs of the members of the international society –
states.

Article 38 ICJ Statute defines customary law, in somewhat lapidary terms, as evidence of a
general practice accepted as law. This is a bit curious (if not all that important) in that the custom is
not, strictly, evidence of a general practice, but rather the other way around; the practice is evidence
that there is a custom. Be this as it may, the definition provides two main requirements: there must
be a general practice, and this general practice must be accepted as law or, as international lawyers
tend to say, the general practice must be accompanied by opinio juris, a sense of legal obligation.
Both requirements have their own complications, and the precise relationship between them is
problematic as well.18

A general practice

Societies differ from one another, and also over time; accordingly, it is difficult to say in the abstract
when a practice is general enough to award it the status of a rule of customary international law. One
would think that the practice of only a handful of states might not really qualify as ‘general’, but this
would be mistaken. There is, for example, the possibility of regional customary law, confirmed as
matter of principle in the 1950 Asylum case.19 There may even be something like a custom between
two states only, although here it might be more appropriate to speak of a set of historic rights and
obligations.20

In earlier days it was sometimes thought that the formation of a customary rule could take quite
some time. Without being very specific, Vattel noted in the eighteenth century that customary law
consisted of customs and maxims ‘consecrated by long use’, which suggests quite a lengthy period
of gestation, possible decades.21 By contrast, the ICJ found in 1969 that ‘even without the passage of
any considerable period of time, a very widespread and representative [practice] might suffice of
itself’.22

Likewise, it cannot be specified, in the abstract, how many instances of practice are required.
Many incidents over a short period of time may be just as forceful as a handful of instances spread
out over a long period of time, or even more so. Much may depend also on the precise issue area; it
seems generally accepted that since there are few space activities to begin with, space law can develop
without too many instances of practice, and it has even been suggested that in such a field ‘instant
custom’ may develop.23 In other walks of life things may be different though; in fields such as the law
of the sea, there is more practice and therefore the demands on a new rule of custom may be
considerably higher.

Another relevant question is whose practice is required. Obviously, landlocked states such as
Austria and Switzerland will not have much practice when it comes to maritime affairs; consequently,
a focus on their practice will not be very revealing. By the same token, the development of customary
space law will owe more to the practices of the USA, Russia and France than those of Sierra Leone
or Norway. Consequently, what matters in particular is that those states whose interests are especially
affected by a customary rule participate in its making.24 If this seems difficult to reconcile with

sovereign equality, none the less given the very nature of custom as the normative reflection of
practice, it could hardly be otherwise. The Belgian jurist Charles de Visscher, a long-time judge at the
ICJ, once made an apt analogy with footprints in the sand; there are always ‘some who mark the soil
more deeply with their footprints than others, either because of their weight, which is to say their
power in this world, or because their interests bring them more frequently this way’.25

Perhaps the most controversial question concerning practice is what exactly counts as practice.
Practice, after all, can take various forms; acting is practice, but so is speaking; philosophically at any
rate, humans act through speech, and a lot also depends on the context. Saying ‘I do’ at a wedding
ceremony is bound to give rise to different expectations from saying ‘I do’ when asked whether one
is enjoying a nice lunch or whether one supports Manchester United.26

It is generally accepted that the material acts of states (thus, actively seizing foreign vessels,
actually expropriating foreign property or sending satellites into orbit) count as elements of state
practice. It is also generally accepted that the legislative acts of states, and their legal practices
generally, may qualify as state practice. Thus, if many states enact a law for the protection of fish
stocks up to 200 miles off their coasts, and if they actively prosecute violators, then at some point the
conclusion may be warranted that this is a general practice with the potential to crystallize into a rule
of customary international law.

More controversial is whether mere statements may qualify as state practice. If state
representatives proclaim before international audiences that the state in question condemns torture, is
this to be counted as state practice, or merely an example of talk being cheap? If the head of
government of a state declares to his parliament that the state will never expropriate foreign property,
is this to be regarded as state practice, or rather as a public statement, without any probative value
unless the state actually enacts a law protecting against expropriation? And what if a state votes in an
international meeting; is voting to be regarded as acting, on the same level as the material act, or is
voting closer to mere speech? In short, the evidences of custom are, and will remain, controversial.

Accepted as law

Complications are compounded by the second main requirement of custom; not only must there be a
general practice, but this practice must also be accepted as law (opinio juris). This makes sense; there
are many practices which are deemed useful or pleasant in one way or another, but which it would be
silly to try and enforce in a court of law, or to ask for compensation upon violation. Thus, it might be
customary to welcome visiting foreign dignitaries by rolling out the red carpet, but few would think
of such a rule as a rule of law; it has force, but has not been ‘accepted as law’. The requirement
of opinio juris therewith plays the useful role of separating law from other normative control systems,
such as etiquette or morality, or of separating legally warranted behaviour from merely politically
expedient behaviour.

How, then, to recognize opinio juris? In fact, often the evidences of opinio juris are identical to
those of state practice; enacting a law, concluding a treaty, engaging in a legal practice may all count
both as evidence of state practice, and as evidence of the sentiment that the behaviour is legally
warranted. In addition, it is generally acknowledged that resolutions adopted by international
organizations (in particular the UN General Assembly, whose resolutions do not formally bind the
UN's membership) or at international conferences may, their non-binding status notwithstanding,
reflect opinio juris.