Sources of international law

AuthorJohn H. Currie, Craig Forcese, Joanna Harrington, Valerie Oosterveld
In the preceding chapter, we def‌ined international law both by focusing on its historical
role as the law of sovereign states and by examining various theories advanced to explain
it. In this chapter we ask the same question — what is international law? from a doc-
trinal perspective. Specif‌ically, here we examine where the rules of international law come
from and in what circumstances they emerge; how one assesses whether a given norm
really is a rule of international law; and how one determines which entities are bound by
any given rule of international law.
The answers to these questions are not simple. As we have already seen, unlike domes-
tic legal systems, there is no clear constitutional structure in the international sphere as-
signing a particular body an exclusive or even principal law-making role. Rather, in keeping
with the predominant role still played by sovereign states in the international system, inter-
national law is generated by complex, decentralized processes. Moreover, when compared
with most domestic legal systems, the international legal system is plagued by a paucity of
dispute resolution mechanisms with the power to determine the content of international
law in a general, binding manner. Thus, the content of international law is more readily
contestable in international relations, and statements of principle are prone to protracted
debates about their precise legal status and ambit. Adding to this complexit y is the fact
that not all states or other international actors are bound by the same rules of international
law. Contrary to popular misconception, international law is not necessarily universal law.
What are the decentralized law-making processes referred to above? This is to ask
about the sources of international law. Asked to list the sources of international law, state
representatives and international legal scholars almost invariably point to Article 38(1) of
the treaty establishing the International Court of Justice (ICJ), the Statute of the ICJ. We
examine the ICJ or World Court at length in Chapter 3. For the present, consider the
manner in which the sources of international law are described in Article 38(1). Is their
description more consistent with positivist or natural law theories? Who, if anyone, ap-
pears to be the dominant player in “producing” each form of international law? What is
the signif‌icance of the closing phrase of Article 38(1)(d)?
Statute of the International Court of Justice, 26 June 1945, Can TS 1945 No 7, in force
24 October 1945
Article 38
(1) The Court, whose funct ion is to decide in accordance with internat ional law such
disputes as are submitted to it, shal l apply:
(a) international conventions, whether general or par ticular, establishing rules ex-
pressly recognized by the contesting st ates;
(b) international custom, as ev idence of a general practice accepted as law;
(c) the general principles of law recognized by c ivilized nations;
(d) subject to t he provisions of Artic le 59 [whic h provides that the decision of the
Court has no binding force except bet ween the parties and in respect of that par ticu-
lar case], judici al decisions and the teachin gs of the most highly qu alif‌ied publicists
of the various nations, as subsidia ry means for the determination of rules of law.
1) The Concept of Treaties
The best known source of international law is the “treaty,” referred to in Article 38(1)(a)
of the Statute of the ICJ as “international conventions, whether general or par ticular . . .”
Examples include: the Charter of the United Nations1 (the constitutive instrument of the
UN); the International Covenant on Civil and Political Rights2 and the International Coven-
ant on Economic, Social and Cultural Rights3 (the two most impor tant multilateral hu-
man rights treaties); the Agreement between the United Nations and the Government of
Sierra Leone on the Establishment of a Special Court for Sierra Le one4 (providing for the
prosecution of serious international crimes committed in Sierra Leone); the Canada-Israel
Free Trade Agreement5 (a bilateral agreement liberalizing trade between the two par ties);
and many others. At the time of writing, Canada is a party to approximately 2,500 treaties
that are in force.
Treaties are, in some sense, international “contracts”6 between states and/or cert ain
international organizations, setting out rules that bind, as a matter of international law,
the parties to them in their relations with one another. These agreements can be bilateral
(between two parties) or multilateral (between more than two par ties).7 Treaties also
go by various names, including: treaty, covenant, protocol, agreement, procès-verbal, ex-
change of notes, exchange of letters, joint communiqué, charter, statute, and more. Article
38(1)(a) of the Statute of the ICJ (itself a treaty, notwithstanding the use of “Statute” in its
title) uses one of the most common terms to refer to a treaty as a source of international
law, namely “convention.” While historical, political, or other reasons may account for the
1 26 June 1945, Can TS 1945 No 7, in force 24 October 1945 [UN Charter].
2 16 December 1966, 999 UNTS 171, Can TS 1976 No 47, in force 23 March 1976 [ICCPR].
3 16 December 1996, 993 UNTS 3, Can TS 1976 No 46, in force 3 January 1976 [ICESR].
4 16 January 2002, 2178 UNTS 137, in force 12 April 2002.
5 31 July 1996, Can TS 1997 No 49, in force 1 January 1997. See also Canada-Israel Free Trade Agreement
Implementation Act, SC 1996, c 33.
6 The domestic law notion of “contra ct” is used only by way of analogy here, and con tracts in the strict
sense should not be confused wit h treaties. An essential distinction bet ween the two is that contracts
are governed by domestic law w hereas treaties are governed by international law.
7 A particular type of multilateral treat y, known as a “plurilateral” treaty, is recognized by some autho rs
and in the practice of some st ates: see for example Anthony Aust, Mod ern Treaty Law and Practic e, 2d
ed (Cambridge: Cambridge Univer sity Press, 2007) at 139 (“The term ‘plurilateral’ . . . de scribes a treaty
negotiated betw een a limited number of states with a partic ular interest in the subject matter”).
Chapter 2 : Sources of International Law 49
use of a particular term as part of a treaty’s title, the international legal effect of a treaty
does not vary depending on the word used to designate it.
In domestic legal systems, the existence of a legally binding contract depends on a
comprehensive body of law governing the creation, operation, and termination of con-
tracts. So too in the international legal system: the creation, operation, and termination of
treaties are governed by a body of international law known as “treaty law,” or the “law of
treaties.” The most notable source of treaty law is itself a treaty: the Vienna Convention on
the Law of Treaties (VCLT), which codif‌ies the most important rules governing the forma-
tion, legal effec ts, and termination of treaties. While the VCLT lacks universal adherence
by states at the time of writing it has 113 states parties, not including key states such as
the United States, France, and India — commentators and states themselves usually re-
gard most of its provisions as ref‌lecting rules of customary international law. We discuss
customary international law in detail below. For present purposes, to the extent the VCLT
ref‌lects rules of customary international law, those rules are binding on all states regard-
less of whether they are, strictly speaking, parties to the VCLT. Most of the VCLT is thus a
convenient reference point for the law of treaties binding on all states.
2) The Legal Essence of Treaties
In the above section we examined in general terms the concept of treaties. We turn now
to a more detailed examination of the essential international legal requirements for treat-
ies. In other words, what are the indispensable features of an agreement if it is to be con-
sidered a “treaty”? Consider f‌irst the following excerpt from the VCLT:
1980 No 37, in force 27 January 1980
Article 1
Scope of the present Convention
The present Convention applies to treaties between States.
Article 2
Use of terms
1. For the purposes of the present Convention:
(a) “treaty” means an inter national agreement concluded between States in written
form and governed by inter national law, whether embo died in a single instrument
or in two or more related instruments a nd whatever its particular designation; . . .
Article 3
International agreements not within the scope of the present Convention
The fact that the present Convention does not apply to international agreements conclud-
ed between States and other subjects of international law or between suc h other subjects
of international law, or to international agree ments not in written form, shall not affect:
(a) the legal force of such agreements;
(b) t he application to them of any of the rules set forth in the present Convention to
which they would be subject u nder international law independently of the Convention;

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