Sources of International Law

AuthorJohn H. Currie; Craig Forcese; Joanna Harrington; Valerie Oosterveld
Sources of International Law
In the preceding chapter, we dened international law both by focusing on its historical role
as the law of sovereign states and by examining various theories advanced to explain its
nature or even existence. In this chapter we ask the same question what is international
law? from a doctrinal perspective. Specically, here we examine where the rules of inter-
national law come from; 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.
Answering these questions is not simple. As we have already seen, unlike most domestic
(that is, national) legal systems, there is no clear constitutional structure in the international
sphere assigning 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, international law is generated by complex, decentralized processes dominated by
states. Moreover, when compared to most domestic legal systems, the international legal
system is plagued by a relative 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 complexity 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 repre-
sentatives and international legal scholars almost invariably point to Article () of the treaty
establishing the International Court of Justice (ICJ), the Statute of the ICJ, which directs the
Court on the legal sources it may apply. We examine the ICJ or World Court at length in
Chapter . For the present, consider the manner in which the sources of international law
are described in Article (). Is their description more consistent with positivist or natural
law theories? Who, if anyone, appears to be the dominant player in “producing” each form
of international law? What is the signicance of the closing phrase of Article ()(d)?
Statute of the International Court of Justice,  June , Can TS  No , in force  October 
Arti cle 
() The Court, whose function is to decide in accordance with international law such
disputes as are submitted to it, shall apply:
Chapter : Sources of International Law 
(a) international conventions, whether general or particular, establishing rules expressly
recognized by the contesting states;
(b) int ernational 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  [which provides that a decision of the Court
has no binding force except between the parties and in respect of that particular case],
judicial decisions and the teachings of the most highly qualied publicists of the vari-
ous nations, as subsidiary means for the determination of rules of law.
) The Concept of Treaties
The best known source of international law is the “treaty,” referred to in Article ()(a) of the
Statute of the ICJ as “international conventions, whether general or particular . . .” In Canada,
the expression “international treaties” is increasingly used to dierentiate these treaties
from those concluded with Indigenous Peoples. The latter give rise to a distinct type of legal
relationship and have constitutional status within Canada, having long been recognized as
“sacred” “exchanges of solemn promises” of “a unique sui generis nature.”
Canada is a party to approximately , international treaties (, bilateral and 
multilateral) that are in force. Examples include the Charter of the United Nations (the multi-
lateral treaty constituting the UN); the International Covenant on Civil and Political Rights and
multilateral human rights treaties); the Cooperation Agreement between the Government of
Canada and the European Space Agency (a bilateral agreement with an international organiz-
ation providing for cooperation in space-related activities); the Canada-Kosovo Foreign Invest-
ment Promotion and Protection Agreement (a bilateral agreement providing protections for
investors from each party in the marketplace of the other); and many others.
Treaties are, in some sense, international “contracts”between states (or certain inter-
national organizations, as suggested in one of the examples cited above) setting out rules
See Government of Canada, “Treaties, Laws and Regulations” (last modied  April ), online:
 See Guerin v The Queen, []  SCR  at ; Simon v The Queen, []  SCR  at , ; Rv
Badger, []  SCR  at . Section () of the Constitution Act, , being Schedule B to the
Canada Act  (UK), expressly recognizes and arms the constitutional status of both the “aborig-
inal and treaty rights of the aboriginal peoples of Canada.” On their pre- role, see Brian Slattery,
“The Hidden Constitution of Canada: Aboriginal Rights in Canada” ()  Am J Comp L .
Numbers provided by the Treaty Law Division at Global Aairs Canada, upon inquiry to Detailed information on treaties in force for Canada is also made publicly
available by the Treaty Law Division online:
 June , Can TS  No , in force  October  .
 December ,  UNTS , Can TS  No , ()  ILM , in force  March  [ICCPR].
 December ,  UNTS , Can TS  No , ()  ILM , in force  January  .
 February , Can TS  No , in force  June .
 March , Can TS  No , in force  December .
The notion of “contract” is used only by way of analogy; contracts should not be confused with treat-
ies. An essential distinction between the two is that contracts are governed by domestic (national) law
whereas treaties are governed by international law.
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 parties). Treaties also go by various names, including treaty, covenant, proto-
col, agreement, procès-verbal, exchange of notes, exchange of letters, joint communiqué,
charter, statute, and more. Article ()(a) of the Statute of the ICJ (itself a treaty, notwith-
standing 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 use of a particular term as part of a treaty’s title, the inter-
national legal eect of a treaty does not depend on the word used to designate it.
In domestic legal systems, the existence of a legally binding contract depends on a com-
prehensive body of (domestic) law governing the creation, operation, and termination of
contracts. 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 codies the most important rules governing the formation, legal
eects, and termination of treaties. While the VCLT lacks universal adherence by states — at
the time of writing it has  states parties, not including key states such as the United States,
France, and India commentators and states themselves usually regard most of its provi-
sions as reecting rules of customary international law. We discuss customary international
law in detail later in this chapter, but for present purposes it suces to note that rules of
customary international law are generally considered to be binding on all states. Thus, to the
extent the VCLT reects rules of customary international law, those rules are binding on all
states regardless 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.
) 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 treaties. In
other words, what are the indispensable features of an agreement if it is to be considered a
“treaty”? Consider rst the following excerpt from the VCLT:
Vienna Convention on the Law of Treaties,  May ,  UNTS , Can TS  No , in
force  January 
Article 
Scope of the present Convention
The present Convention applies to treaties between States.
Article 
Use of terms
. For the purposes of the present Convention:
 A particular type of multilateral treaty, known as a “plurilateral” treaty, is recognized by some authors
and in the practice of some states: see for example Anthony Aust, Modern Treaty Law and Practice, d
ed (Cambridge: Cambridge University Press, ) at  (“The term ‘plurilateral’ . . . describes a treaty
negotiated between a limited number of states with a particular interest in the subject matter”) [Aust].

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