The Law of Treaties

• Author: John H. Currie
• Pages: 123-184

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Chapter 4

THE LAW OF TREATIES

a. Nature aNd importaNCe of treaties

As described above,1 treaties are express and usually formalized agree-

ments between states or other subjects of international law — they set

out the parties’ mutual legal rights and obligations, and are governed

by international law. They may take the form of reciprocal undertak-

ings between as few as two states (“bilateral” treaties), or more gen-

eralized agreements adhered to by several or even, on occasion, most

states in the world (“multilateral” treaties). Their subject matter ranges

from very specif‌ic undertaking-and-performance agreements between

states — akin to domestic law contracts and therefore sometimes called

“treaty-contracts” — to broad codif‌ications or restatements of certain

substantive areas of international law, designed to govern the ongoing

conduct of all the parties to them in the relevant subject-area (some-

times called “law-making” or “codif‌ication” treaties).

Treaties are thus supple legal tools in the hands of states, permit-

ting them to enter into individual relationships with other states on

very specif‌ic issues or projects, or to establish widely applicable norms

intended to govern legal relationships with as many other states as will

expressly agree to their terms. Indeed, in the twentieth and twenty-f‌irst

centuries states have even made use of treaties to reshape and redef‌ine

the structure of the international legal system itself. For example, the

1 See Chapter 3, Sect ion C(2).

PUBLIC INTERNATIONA L LAW124

United Nations (UN), with its enormous institutional apparatus (in-

cluding the International Court of Justice), is merely the product of

one of the most successful and widely ratif‌ied multilateral treaties of

all time, the Charter of the United Nations and its annexed Statute of the

International Court of Justice.2

Thanks largely to such institutional innovations, treaties have had

pride of place in developing and clarifying international law in the past

century. Previously, customary international law was clearly the pri-

mary source of generally applicable international norms, early treaty

practice being largely bilateral and situation-specif‌ic in nature. This

began to change in the late nineteenth and early twentieth centuries

with the elaboration of broader-based treaty regimes, mostly concerned

with the conduct of war and humanitarian law.3 The last half of the

twentieth century, however, witnessed explosive growth in the number

of multilateral codif‌ication or law-making treaties in virtually all areas

of the law.

As suggested above, this phenomenal growth can be attributed

partly to the establishment of international institutions such as the

United Nations and its agencies, which have provided permanent fora

for the negotiation of such broad-based agreements.4 Of particular im-

portance to this process has been the work of the International Law

Commission (ILC), a panel of experts established by the General As-

sembly of the United Nations in 1947 in partial fulf‌ilment of its mandate

to “encourage the progressive development of international law and its

codif‌ication.”5 The ILC has been at the forefront of the “codif‌ication”

movement, steadily producing draft texts in a variety of f‌ields, texts

that have served as the starting point for state negotiations leading to

the conclusion of some of the most successful multilateral treaties.6

The rise in the relative importance of treaties as a source of gener-

ally applicable international law can also in part be attributed to the

2 Charter of the United Nat ions,26 June 1945, Can. T.S. 1945 No. 7 (entered into

force 24 October 1945) [UN Charter]; Statute of the Interna tional Court of Justice,

26 June 1945, Can. T.S. 1945 No. 7 (entered into force 24 October 1945) [ICJ

Statute].

3 For example, Convention for th e Pacif‌ic Settlement of Interna tional Disputes

(Hague I), 29 July 1899, reproduced in J.B. Scott, The Hague Peace Conferen ces of

1899 and 1907, vol. II (New York: Garland, 1972) at 80; and Convention Respe ct-

ing the Laws and Customs of War on Lan d (Hague IV), 18 October 1907, repro-

duced in ibid. at 368.

4 See O. Schachter, “United Nat ions Law” (1994) 88 A.J.I.L. 1 at 1–2.

5 UN Charter, above note 2, Art icle 13(1). See also Chapter 3, Section D(2).

6 For a more thorough overview of the mandate, procedure, and work of the ILC,

see the Intern ational Law Commis sion’s homepage, online: www.un.org/la w/ilc/.

The Law of Treaties125

peculiar advantages offered by treaties as law-making devices. These

include the speed and clarity with which the law may be codif‌ied, cre-

ated, or advanced, which has been important in accommodating the

dramatically increased intensity and breadth of international discourse

since the Second World War.

Given their requirement of express consent, moreover, treaties

dovetail neatly with positivist notions of the source of binding obliga-

tion in international law. They represent the ultimate embodiment of

the theory of consent and thus of the sovereignty of states.7 As such,

states may feel they are “taking charge” of their own legal obligations

by participating in multilateral treaty negotiations, thus providing yet

more momentum to the multilateral treaty juggernaut.

Numerous terms have been coined to refer to treaties in one form or

another, the most common of which include “conventions,” “charters,”

“covenants,” “protocols,” “pacts,” “acts,” “statutes,” or, simply, “agree-

ments.” While various factors will inf‌luence states in their choice of

title for any particular treaty, the term used has no legal signif‌icance in

itself. All treaties, whatever their designation, and as long as they rep-

resent the express will of the parties to be bound by their terms in ac-

cordance with international law, are equally binding upon the parties.

b. the

vieNNa CoNveNtioN oN the law

of treaties

It is one of the ironies of international law that the legal rules governing

the formation, legal effects, and dissolution of treaties have for the most

part evolved as a matter of customary international law.8 Through the

centuries states have, by their conduct and attitude, conf‌irmed that an

express agreement between them must be honoured in good faith. They

7 See Chapter 3. Even th is most positivist of form al international lega l sources

has a natur al law seam runni ng through it, however. Although states ar e only

bound by treat ies to which they expressl y consent, once that consent is un -

conditionall y given it cannot unilatera lly be withdrawn. The f undamental rule

that treat ies must be performed in good f aith (see Section G(1), below in this

chapter) is a clear derogat ion from the theory of consent: s ee above Chapter 3,

Section C(2).

8 The role of domestic law is of cou rse also important i n the treaty formation

process, but th is chapter focuses on the inte rnational legal ru les governing

treaties. The s ignif‌icance of domestic cons titutional orders on treat y formation

and implementat ion will be discuss ed in Sections G(1) and I(2)(a), below in this

chapter, as well as i n Chapter 6.