Many international disputes are concerned with the interpretation and effects of international agreements, that is, treaties, and much of the practical content of state relations is embodied in and structured by treaties. International organizations, including the United Nations, have their legal basis in multilateral treaties. So too do arrangements on matters ranging from geostationary orbit to the regulation of intellectual property to the governance of Antarctica. Networks of bilateral treaties regulate such matters as aviation, boundaries, extradition, investment protection, and shared natural resources.

Since 1949 the ILC has concerned itself with the law of treaties.2 In 1966 it adopted a set of 75 draft articles:3these formed the basis for the 1969 Vienna Convention on the Law of Treaties (VCLT), which entered into force on 27 January 1980.4

The European Court of Justice has observed that the customary international law of treaties forms part of the European legal order, and it generally follows the VCLT (implicitly or explicitly);8 the WTO dispute settlement body has also emphasized the customary status of the VCLT rules of treaty interpretation.9

The Convention was adopted by a very substantial majority at the Vienna Conference10 and covers the main areas of the law of treaties. It does not deal with (a) treaties between states and organizations, or between two or more organizations;11 (b) state succession to treaties;12 or (c) the effect of armed conflict on treaties,13 each of which has been the subject of separate ILC projects.

References(p. 369) (A)  Definition of ‘Treaty’

The reference to ‘other subjects’ of the law was designed to provide for treaties concluded by international organizations, the Holy See, and other international entities. But the ILC’s Final Draft, and the VCLT itself, are confined to treaties between states (Article 1).15 Article 3 provides that the fact that the Convention is thus limited shall not affect the legal force of agreements between states and other subjects of international law or between such other subjects.

Article 2(1)(a) defines a treaty as ‘an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation’. The distinction between a transaction which is a definitive legal commitment between two states, and one which involves something less than that is difficult to draw. But the form or title of the instrument, for example, a joint communiqué, is not decisive.16

Article 2(1)(a) also stipulates that the agreements to which the Convention extends must be ‘governed by international law’; this excludes commercial arrangements made between governments under one or more national laws.17

(B)  The Functions of Treaties

McNair long ago pointed to the variety of functions which treaties perform.18 Some treaties, dispositive of territory and rights in relation to territory, are like conveyances.References(p. 370) Treaties involving bargains between a few states are like contracts; whereas the multilateral treaty creating either a set of rules, such as the Hague Conventions on the Law of War, or an institution, such as the Copyright Union, is ‘law-making’. The treaty constituting an institution is akin to a charter of incorporation. It is certainly fruitful to contemplate the different features of different kinds of treaties and even to expect the development of specialized rules. Thus the effect of war between parties varies according to the type of treaty involved. However, McNair and others have tended to support the position that the genus of treaty produces fairly general effects on the applicable rules. Thus the lawmaking character of a treaty is said (a) to rule out recourse to preparatory work as an aid to interpretation; (b) to avoid recognition by one party of other parties as states or governments; and (c) to render the doctrine of rebus sic stantibus inapplicable.19

By contrast the ILC deliberately avoided any classification of treaties along broad lines and rejected the concept of the ‘objective regime’ in relation to the effects of treaties on non-parties. It accepted specialized rules in a few instances,20 but did not consider it necessary to make a distinction between ‘law-making’ and other treaties.21 The ILC and in turn the Vienna Conference saw the law of treaties as essentially a unity.22Moreover jurists are now less willing to accept categorical distinctions between treaty-contract (vertrag) and treaty-law (vereinbarung).23 The contrast intended between the bilateral political bargain and the ‘legislative act’ produced by a broad international conference does not correspond to reality. Political issues and bargaining lie behind law-making efforts like UNCLOS III. Further, the distinction obscures the real differences between treaty-making and legislation in a municipal system. Nonetheless, it should be acknowledged that some of the VCLT rules, for example Article 18 and the rules relating to reservations, may work better with contractual-type agreements than with law-making ones.

(C)  Participation in Treaties

In an early draft the ILC defined a ‘general multilateral treaty’ as ‘a multilateral treaty which concerns general norms of international law and deals with matters of general interest to States as a whole’.24 But which states and other entities are permitted to participate in drawing up such a treaty is a matter for the proponents, or in the case of a treaty concluded under the auspices of an international organization, the organization. In the ILC it was proposed that states should have a right to become parties to this type of treaty, a solution adopted in the insubstantial form that the right existed except where the treaty or the rules of an international organization (p. 371) provided otherwise.25 The ILC’s Final Draft contained no provision on the subject and amendments intended to give ‘all States a right to participate in multilateral treaties’ were defeated at the Vienna Conference.26

(A)  Form and Intention27

How treaties are negotiated and brought into force depends on the intention of the parties. There are no overriding requirements of form:28 for example, an agreement recorded in an exchange of letters or even the minutes of a conference may have the same legal effect as a formally drafted treaty contained in a single instrument.29 In practice form is governed partly by usage, and will vary according to whether the agreement is expressed to be between states, heads of states, governments, or particular ministers or departments. The VCLT applies only to agreements ‘in written form’ but Article 3 stipulates that this limitation is without prejudice to the legal force of agreements ‘not in written form’.30

Where the parties wish to record mutual understandings for the conduct of their business or other relationships, but do not intend to create legally binding obligations, they often conclude non-binding instruments commonly referred to as memoranda of understanding (MOUs).31 The name of the instrument is not conclusive as to its legal status, however; what matters is the intention of the parties as reflected in the terms of the instrument.32

(B)  Full Powers and Signature33

One example of full powers arose in Land and Maritime Boundary between Cameroon and Nigeria, with the Court confirming that the full powers afforded to a head of state derive from his or her position at the top of a state’s hierarchy.35 This position was expanded upon—beyond the law of treaties—in Genocide, with VCLT cited for the proposition that ‘every Head of State is presumed to be able to act on behalf of the State in its international relations’.36

The successful outcome of negotiation is the adoption and authentication of an agreed text. Signature has, as one of its functions, authentication, but a text may be authenticated in other ways, for example by incorporation in the final act of a conference or by initialling.37

Where the signature is subject to ratification, acceptance, or approval, signature does not establish consent to be bound nor does it create an obligation to ratify.38 What it does is to qualify the signatory to proceed to ratification, acceptance, or approval; it also creates an interim obligation of good faith to refrain from acts calculated to frustrate the objects of the treaty.39

Where the treaty is not subject to ratification, acceptance, or approval, signature establishes consent to be bound. Sometimes signature may be dispensed with: the text may be adopted or approved by resolution of the UN General Assembly and submitted to member states for accession.

(C)  Ratification

Ratification involves two distinct procedural acts: the first an internal act of approval (e.g. by the parliament, or the Crown in the UK); the second the international procedureReferences(p. 373) which brings a treaty into force by a formal exchange or deposit of instruments of ratification. Ratification in the latter sense is an important act involving consent to be bound.40 But everything depends on the intention of the parties, and modern practice contains many examples of less formal agreements intended to be binding on signa-ture.41 As to the small number of treaties containing no express provision on ratification, the ILC initially considered that ratification should be required.42 However, it changed its view, partly because of the difficulty of applying the presumption to treaties in simplified form. VCLT Article 14 regulates the matter by reference to the parties’ intention without any presumption.

(D)  Accession, Acceptance, and Approval

‘Accession’ occurs when a state which did not sign a treaty formally accepts its provisions: this may be before or after the treaty has entered into force. The conditions for accession and the procedure involved depend on the provisions of the treaty. Accession may be the only means of becoming a party, as in the case of a convention approved by the General Assembly and proposed for accession by member states.43 Recent practice has introduced the terms ‘acceptance’ and ‘approval’ to describe the substance of accession. Terminology is not fixed, however, and where a treaty is expressed to be open to signature ‘subject to acceptance’, this is equivalent to ‘subject to ratification’.

(E)  Other Expressions of Consent to be Bound

These are not the only means by which consent to be bound may be expressed. Other means may be agreed, for example an exchange of instruments constituting a treaty.44

(F)  Entry into Force, Deposit, and Registration

The provisions of the treaty determine how and when the treaty enters into force. Where the treaty does not specify a date, there is a presumption that the treaty comes into force as soon as all the negotiating states have consented to be bound.45

After a treaty is concluded, the written instruments of ratification, accession, etc and also reservations and other declarations are placed in the custody of a depositary,References(p. 374) which may be one or more states or an international organization.46 The UN Secretariat plays a significant role as depositary of multilateral treaties.

Article 102 of the UN Charter provides as follows:

1. 
   

   1.  Every treaty and every international agreement entered into by any Member of the United Nations aft er the present Charter comes into force shall as soon as possible be registered with the Secretariat and published by it.

   
   
2. 
   

   2.  No party to any such treaty or international agreement which has not been registered in accordance with the provisions of paragraph 1 of this Article may invoke that treaty or agreement before any organ of the United Nations.

This provision (which goes back to President Woodrow Wilson)47 is intended to discourage secret diplomacy and to promote the availability of treaty texts. The Secretariat accepts agreements for registration without conferring any status on them or the parties which they would not have otherwise. However, this is not the case where the regulations provide for ex officio registration. This involves initiative by the Secretariat and extends to agreements to which the UN is a party, trusteeship agreements, and multilateral agreements with the UN as depositary. The phrase ‘every international agreement’ has a wide scope. Technical intergovernmental agreements, declarations accepting the optional clause in the Statute of the International Court, agreements between organizations and states, agreements between organizations, and unilateral engagements of an international character are included.48

Non-registration does not affect the validity of agreements, but these may not be relied upon in proceedings before UN organs. In relation to the similar provision in the Covenant of the League the view was expressed that an unregistered agreement could be invoked if otherwise appropriately publicized.49

VCLT Article 2(d) defines a reservation as ‘a unilateral statement, however phrased or named, made by a State, when signing, ratifying, accepting, approving or acceding toReferences(p. 375) a treaty, whereby it purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that State’. It is to be distinguished from an interpretative declaration, which is an expression of view by a declarant state as to the meaning of a treaty which is not put forward as a condition of being bound.51

Considerable uncertainty has surrounded the law and practice with regard to reservations.

(A)  Historical Background

League of Nations practice in regard to multilateral conventions lacked consistency. The League Secretariat, and later the UN Secretary-General, as depositary of conventions concluded under the auspices of the League, followed the principle of absolute integrity: a reservation would only be valid if the treaty permitted it or all contracting parties accepted it; otherwise the reserving state would not be considered a party.52 In contrast the Pan-American Union, later the Organization of American States, adopted a flexible system which permitted a reserving state to become a party vis-à-vis non-objecting states. This system, dating from 1932, promotes universality at the expense of consistency of obligation.

Following the adoption of the Genocide Convention in 1948, a divergence of opinion arose on the admissibility of reservations to the Convention, which contained no provision on the subject; an advisory opinion was sought. The International Court stressed the divergence of practice and the special characteristics of the Convention, including the intention of the drafters that it be universal in scope. The Court’s principal finding was that ‘a State which has made…a reservation which has been objected to by one or more of the parties to the Convention but not by others, can be regarded as being a party to the Convention if the reservation is compatible with the object and purpose of the Convention’.53

In 1951 the ILC rejected the ‘compatibility’ criterion as too subjective, preferring a rule of unanimous consent.54However, in 1952 the General Assembly requested the Secretary-General to conform practice to the opinion of the Court and, in respect ofReferences(p. 376) future conventions of which the Secretary-General was depositary, to leave it to each state to draw its own conclusions from reservations communicated to it.55 In 1959 the General Assembly extended this to cover all UN conventions, unless they contained contrary provisions.56 In 1962 the ILC decided in favour of the ‘compatibility’ rule.57

(B)  Impermissible Reservations

VCLT Article 20 provides for acceptance of and objection to reservations other than those expressly authorized by a treaty.58 The ‘compatibility’ test is by no means ideal;59 in particular its application is a matter of appreciation, left to individual states. How is the test to apply to provisions for dispute settlement, for example? In practical terms the ‘compatibility’ test may not sufficiently maintain the balance between the integrity and the effectiveness of multilateral conventions in terms of a firm level of obligation. It is very doubtful whether there can be any place for the ‘compatibility’ test in relation to unlawful reservations.60

The issue of severability in relation to human rights treaties has been particularly controversial.61 In Belilos62and Loizidou63 the European Court of Human Rights treated the objectionable reservation as severable. So did the Human Rights Committee: a state could not, for example, reserve the right to subject persons to torture, or to presume a person guilty unless proven innocent;64 rather than the state’s participation in the treaty being negated, it was held to be a party to the treaty without benefit of its reservation, whatever its underlying intention may have been.

(C)  The ILC Guide (2011)

Some of the difficulties in respect of permissibility of reservations are addressed in the comprehensive Guide to Practice on Reservations to Treaties adopted by theReferences(p. 377) ILC in 2011, the culmination of 15 years of work.65 The Guide is intended as a ‘toolbox’ for practitioners in dealing with the permissibility and effects of reservations, pointing them towards solutions consistent with existing rules. The Guide is not a binding instrument and is not intended to form the basis of a convention66 but it is likely to make a significant contribution to clarification of law and practice in this area.

On the question of severability the Guide adopts an ingenious intermediate solution. Under Guideline 4.5.1, an invalid or impermissible reservation is null and void, and has no legal effect. Practice has varied on whether the author of an invalid reservation remains bound by the treaty without the benefit of the reservation, or whether the nullity of the reservation vitiates that party’s consent to be bound altogether.67 The Guide provides a presumption that the former applies, unless the contrary intention of that party is expressed or otherwise established.68 In this way the Guide affirms that the key to the status of the reserving party in relation to the treaty is that party’s intention,69 and offers ‘a reasonable compromise between the underlying principle of treaty law—mutual consent—and the principle that reservations prohibited by the treaty or incompatible with the object and purpose of the treaty are null and void’.70

(A)  Pacta Sunt Servanda

The VCLT entails a certain presumption as to the validity and continuance in force of a treaty.71 This may be based upon pacta sunt servanda as a general principle of international law: a treaty in force is binding upon the parties and must be performed by them in good faith.72 Legally, treaties are enduring instruments, not easily disposed of.73 Internal law may not be invoked to justify a failure to perform a treaty.74

References(p. 378) (B)  Application of Treaties

Treaties are not retroactive; that is, unless a contrary intention is established, parties are only bound in respect of acts or facts taking place after the treaty has entered into force for the party in question.75 Unless otherwise stated, they apply within the whole territory of the states parties.76

VCLT Article 30 covers the application of successive treaties to the same subject-matter.77 The relation of treaties between the same parties and with overlapping provisions is primarily a matter of interpretation, aided by presumptions. Thus it is to be presumed that a later treaty prevails over an earlier treaty concerning the same subject-matter. A treaty may provide expressly that it is to prevail over subsequent incompatible treaties; Article 103 of the UN Charter goes further by providing that in the case of conflict, obligations under the Charter prevail over obligations arising under any other international agreement. Article 351 of the Treaty on the Functioning of the European Union (TFEU) provides that pre-existing rights and obligations shall not be affected by its provisions or those of the Treaty on European Union (TEU), but that where incompatibilities exist, parties shall take appropriate steps to eliminate them.78 Whether or not there is a conflict in a given case is of course a matter of interpretation: thus a resolution which is capable of being performed in a manner consistent with the International Covenant on Civil and Political Rights, for example, may be construed as not intending to override the relevant rights.79 VCLT Article 59 provides for the termination or suspension of a treaty in certain circumstances where all parties have concluded a later treaty relating to the same subject-matter.

(C)  Interpretation of Treaties80