1 International law relating to treaties has largely been codified in the Vienna Convention on the Law of Treaties (1969) (‘VCLT’). For the purposes of the VCLT, a ‘treaty’ is defined 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’ (Art. 2(1)(a); see paras 16–19 below).
2 The present article is principally concerned with the law of treaties within the confines of the VCLT, taking also into account the relevant rules of customary international law. Treaties need to be regarded in a wider context; they constitute the major mechanism for the development of legally binding norms among States. To the extent such norms become binding on the national level or determine the content of national law their legitimacy has been put into question (International Law and Domestic (Municipal) Law).
3 An agreement between a State and a non-State entity does not constitute an international treaty, although such an agreement may be governed by international law and may regulate international law issues (see para. 19below).
B. Scope and Development of Treaties
1. Formal Requirements
4 The concept of a treaty in general international law is, in fact, broader than the definition of a treaty for the purposes of the VCLT, and includes treaties between States and international organizations (see para. 13below). The concept of an ‘international treaty’ is also wider than the VCLT definition of a treaty, as it includes oral agreements which, though extremely rare between States, are recognized as binding under the rules of customary international law.
5 Within the terms of the 1969 VCLT, treaties may take an infinite number of forms, from the most elaborately drafted, and formally executed document, to a mere exchange of notes. A broad concept of the definition of treaties was already advocated by the International Law Commission (ILC), which, when defining the notion, stated that an agreement concluded by exchange of notes, exchange of letters, agreed minutes, joint declarations, or other instrument may constitute a treaty (UN ILC ‘Report of the International Law Commission to the General Assembly Covering the Work of its Fourteenth Session’ [24 April–29 June 1962]  vol II UNYBILC 157, 161). This view is also reflected in international jurisprudence. The International Court of Justice (ICJ) in the South West Africa/Namibia (Advisory Opinions and Judgments) (South-West Africa Cases [Ethiopia v South Africa; Liberia v South Africa] [Preliminary Objections]  ICJ Rep 319) stated ‘terminology is not a determinant factor as to the character of an international agreement or undertaking’ (at 331). In Aegean Sea Continental Shelf Case (‘Aegean Sea Case’) it affirmed that ‘it knows of no rule of international law which might preclude a joint communiqué from constituting an international agreement’ (at 39). In the 1994 Maritime Delimitation and Territorial Questions between Qatar and Bahrain (Qatar v Bahrain) (‘Case between Qatar and Bahrain: 1994’) the ICJ considered the value of minutes as an international agreement in the light of Art. 2(1)(a) VCLT and concluded that minutes ‘constitute an international agreement creating rights and obligations for the Parties’ (at 122). Treaties may be bilateral, between two States only, or multilateral, between three or more States including the so-called ‘universal treaties’ to which, at least as a matter of aspiration, all States are intended to be parties (see paras 22–28 below).
3. Normative Treaties, Traités-Lois, and Traités-Contrats
8 Regarding the content of treaties, a distinction is sometimes made between so-called ‘law-making’ or ‘normative’ treaties and ‘contract’ or ‘reciprocal’ or ‘synallagmatic’ treaties (at one time these two categories of treaty were frequently referred to, respectively, as traités-lois and traités-contrats). Normative or contractual treaties are considered to further community interests by setting up international standards which are best achieved by universal participation and are not based on the principle of reciprocity. These standards have been described by ILC Special Rapporteur Pellet as being created, above all, to institute common international regulation on the basis of shared values (UN ILC ‘Report of the International Law Commission Covering the Work of its Forty-Eighth Session’ [6 May–26 July 1996] GAOR 51st Session Supp 10, 81). They constitute a divergent category, consisting of conventions codifying private international law, International Labour Organization (ILO) conventions, treaties on the law of armed conflict, trade and the environment, and human rights treaties. Contractual or reciprocal treaties, on the other hand, are seen to further the individual interests of the participating States, aiming at their mutual benefit which is best achieved through reciprocal obligations (do ut des). However, Pellet and the ILC observed that treaties are rarely entirely normative or entirely synallagmatic (reciprocal) (UN ILC ‘Report of the International Law Commission Covering the Work of its Forty-Ninth Session’ [12 May–18 July 1997] GAOR 52nd Session Supp 10, 47). In most cases, including human rights treaties, they contain both contractual clauses providing for reciprocal rights and obligations as well as ‘normative’ clauses. The term ‘normative treaty’ is therefore generally used to refer to one in which the provisions of a normative character dominate.
4. The Historic Development of Treaties
9 Since ancient times, political entities have used treaties as a tool to shape their international or neighbourly relations. First examples of such instruments go back to the third millennium BC. In antiquity, law and religion were closely related, belonging to the same domain of morals. For example, religious elements were present in the ceremony relating to the conclusion of treaties. An oath was sworn at the conclusion of treaties. As a consequence, God(s) witnessed the legal undertakings and their performance so that a breach thereof would result in a religious sanction. Historically, the most important role was fulfilled by peace treaties. They originated many basic principles, which were later refined by States through general treaty practice.
10 An important step in the historical development of treaties has been the emergence of multilateral treaties. At first, multilateral agreements were concluded in the form of a set of bilateral treaties without any express link between them. The Peace of Westphalia is an example of this and is considered the prototype of the first multilateral treaty (Westphalia, Peace of ). The first multilateral agreement in the form of a single instrument was the Final Act of the Vienna Congress (1815) which summarized the transactions of the Congress (Acte du Congrès de Vienne, signé le 9 Juin 1815 in GF de Martens [ed] Supplément au Receuil des Principaux Traités d’Alliance, de Paix, de Trêves, de Neutralité, de Commerce, de Limites, d’Échange etc. [Librairie de Dieterich Gottingue 1818] vol 6, 379).
5. Codifications of the Law of Treaties
11 The codification of the law of treaties started in the 20th century (Codification and Progressive Development of International Law). In 1928 the American States adopted the Havana Convention on the Law of Treaties (International Conference of American States ‘Convention on Treaties’  29 AJIL Supp 1205). In 1935 the Harvard Draft Convention on the Law of Treaties (Harvard Law School ‘Draft Convention on the Law of Treaties’  29 AJIL Supp 653) was published as part of the ‘Harvard Research in International Law’. After World War II the process of codification was continued on a more formal basis by the ILC, whose work was consummated in the major codifications of the Vienna Conventions (Vienna Convention on the Law of Treaties [‘VCLT’]; Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations [‘VCLT-IO’]; Vienna Convention on Succession of States in Respect of Treaties [‘VCSS-T’]).
(a) The 1969 Vienna Convention on the Law of Treaties (VCLT)
12 The VCLT was the result of the work of the ILC and of the 1968 and 1969 United Nations (UN) Conference on the Law of Treaties. It entered into force on 27 January 1980. The VCLT has been taken to reflect, in general, customary international law in its substantive provisions, although, at the time of its entry into force, some doubts were raised as to the customary international law status of some of its provisions, such as Arts 34–38 (treaties and third States) and Arts 65–68 (procedure in case of alleged invalidity or suspension of treaties), which probably still do not represent customary international law. Art. 73 VCLT states that its ‘provisions…shall not prejudge any question that may arise in regard to a treaty arising from a succession of States or from the international responsibility of a State or from the outbreak of hostilities between States’, issues which were left outside its scope.
(b) The 1978 and 1986 Vienna Conventions (‘VCSS-T’ and ‘VCLT-IO’)
13 There are two further Vienna Conventions which relate to the law of treaties: the 1978 VCSS-T on the succession of States in respect to treaties and the 1986 VCLT-IO, which deals with treaties between States and international organizations or between international organizations themselves. The VCLT-IO adapts the rules of the VCLT to treaty relations concerning international organizations. The VCSS-T is in force, though not all of its provisions are considered to represent customary international law. The VCLT-IO, on the other hand, has not entered into force, though its rules are generally considered to constitute customary international law.
6. Extent of the Binding Force of Treaties
14 The general rule under the law relating to treaties, whether bilateral, contractual, or reciprocal, treaties or multilateral normative treaties, is that they are legally binding for their parties. They are binding, however, only for their parties. There are limited exceptions to this general principle (see paras 97–101 below). Apart from that, treaties which are the constitutive instrument of an international organization can be seen as implying a special normative relevance in relation to non-member States in that the organization may have an objective international legal personality (Obligations erga omnes), as indicated in 1949 by the ICJ in Reparation for Injuries Suffered in the Service of the United Nations (Advisory Opinion) ( ICJ Rep 174).
15 Treaties may also extend their normative relevance beyond their actual parties and the scope of their operation through the influence they may have on the development of new rules of customary international law through State practice (including the practice of non-parties to a treaty). In the North Sea Continental Shelf Cases (Federal Republic of Germany/Denmark; Federal Republic of Germany/Netherlands) ( ICJ Rep 3), the ICJ illustrated the conditions under which such a process may take place. The ICJ observed, first, that the provision concerned should be of a fundamentally norm-creating character, such as could be regarded as forming the basis of a general rule of law; and, secondly, that a very widespread and representative participation in the convention might suffice of itself, provided it included those States whose interests were specifically affected, even without the passage of any considerable period of time. The ICJ further explained the relationship between customary international law and the law of treaties in the 1986 Military and Paramilitary Activities in and against Nicaragua Case (Nicaragua v United States of America) (‘Nicaragua Case’) in which it particularly focused on the parallel existence of treaty rules and rules of customary international law with the same or similar obligations. In such cases, the ICJ stated, the treaty continues to operate as between the parties to it, while the parallel relations between non-parties, or between non-parties and parties, are governed by the corresponding customary international law.
D. Formulation of Treaties
29 States may adopt any procedure they choose to bring a legally binding agreement into existence between them. However, in the absence of any other agreement, the elaborate procedures set out in the VCLT apply; these procedures reflect the practice which had developed between States before the codification of the law in the VCLT.
30 Broadly, this procedure may be divided into two parts. First comes the procedure of negotiation and adoption of the text of a treaty (see paras 31–37 below), and secondly the formal procedure whereby States express their consent to be bound by that text (see paras 52–55 below). This, it may be observed here, generally but not invariably, involves a two-step procedure, consisting of first, the signature of the treaty, and second, its ratification.
2. Treaty Negotiations and the Adoption of a Text
31 The first stages in the formulation of a treaty consist of discussions and negotiations at which the subject matter to be included in the treaty is agreed and a draft text is prepared. There is no particular form prescribed for treaty negotiations, which can be oral, in written form, or both. In the case of bilateral treaties, discussions and negotiations are generally initiated at the level of the parties themselves, and can be conducted at different levels, by Heads of State[s] or Governments, by Ministers of Foreign Affairs or, more often in diplomatic practice, at the level of officials (Heads of Governments and Other Senior Officials).
32 The negotiation of multilateral treaties is often instigated not by States, but by international organizations, such as the UN, International Maritime Organization (IMO), Food and Agriculture Organization of the United Nations (FAO), ILO, or United Nations Educational, Scientific and Cultural Organization (UNESCO). Many international treaties have been prepared by the ILC (such as the VCLT).
33 Conferences have their own rules of procedure (Conferences and Congresses, International). Art. 9 (2) VCLT gives a default rule according to which a convention may be normally adopted at an international conference by a two-thirds majority. The classical rule was that of unanimity, which proved to be a stumbling block in the adoption of multilateral treaties. The two-thirds majority rule, however, may lead to not taking into account minority interests. An alternative practice has developed according to which the text of a treaty can be adopted by consensus, ie without resorting to a vote, and in the absence of a formal objection to follow this course of action. This has a significant impact upon the format of conference deliberations.
34 The formal document summarizing the proceedings of a diplomatic conference and recording its results is called a final act. It usually mentions the purpose of the conference, lists the participating States, and includes the text of the adopted treaty as an attachment.
35 The negotiation of treaties at conferences involves great organizational and administrative tasks which frequently are exercised by the secretariat of the organization sponsoring the conference (International Organizations or Institutions, Secretariats). This includes enabling a smooth running of the negotiations by providing for instant translation and interpretation services, and the distribution of relevant documents. This may also include more substantial tasks such as the preparation of background studies, or participation in drafting an initial negotiation text. It may also take the form of influencing the topics on the agenda of meetings, advising on how to negotiate difficult issues or facilitating the brokering of compromises and agreements. Sometimes, secretariats, de facto, exercise a significant influence on the content of an international treaty.
(b) Adoption and Authentication of the Text
36 The processes of adoption and authentication of the text of a treaty may take any form agreed by the parties (Arts 9, 10 VCLT). In the case of the text of a multilateral treaty adopted at a formal diplomatic conference, this will generally be by way of the inclusion of the text in the final act of the conference (see para. 35above).
37 The adoption and authentication of a text, whether by way of its incorporation in the final act of a conference or by other means, may involve the signature, or initialling, either of the final act, or of the text (see Arts 9, 10 VCLT). But such a signature is not to be confused with what may be a second signature of the treaty for the purposes of signifying a State’s consent to be bound by it, which is part of the second stage in the formation of a treaty covered in paras 52–55 below (and governed by Art. 12 VCLT). Such a signature for authentication does not amount to an expression of consent to be bound, nor does it commit a State to consider signing and/or ratifying the treaty. In the interim period between the signature of an international treaty, a State is under the obligation not to defeat the object and purpose of a treaty it has signed (see para. 48below).
3. Competence to Bind a State
One important issue in the conclusion of treaties, is the question of so-called ‘full powers’, defined in Art. 2(1)(c) VCLT
as a: Theholder of full powers is authorized to adopt and authenticate the text of a treaty and express consent of the State to be bound by a treaty (Treaty-Making Power
). There are a growing number of treaties, in particular bilateral treaties, which do not require the production of full powers (eg exchange of notes).
39 The general rule in Art. 7(1)(a) and (b) VCLT, is that a person is considered as representing a State if he or she produces appropriate full powers or if it appears from the practice of the States concerned, or from other circumstances, that their intention was to consider that person as representing the State and to dispense with full powers. There is, however, a group of persons who by virtue of their functions are considered to have such authority, these being: Heads of States, Heads of Governments, and Ministers of Foreign Affairs, Heads of Diplomatic Missions (for the purpose of the adoption of the text of a treaty between the accrediting State and the State to which they are accredited); and representatives accredited by States to an international organization or one of its organs (for the purpose of adopting the text of a treaty in that conference, organization, or organ) (Art. 7(2) VCLT). Full powers have to be distinguished from credentials, which are submitted to an international organization or a government hosting a conference by a delegate attending to negotiate a multilateral treaty and to sign a Final Act. Signing a treaty itself requires full powers or specific instructions from government.
40 When an unauthorized person purports to conclude a treaty, Art. 8 VCLT provides that the action is without legal effect, unless subsequently confirmed by the State in question. On the other hand, Art. 47 VCLT provides that where an authorized representative of a State expresses consent to be bound, although instructed by a State not to do so, such a conduct does not invalidate this consent, unless the limitation in his or her authority was notified to other negotiating States.
4. Expression of Consent to be Bound
(a) What is Meant by Consent to be Bound
41 A State’s ‘consent’ or ‘intention’ to be bound by a treaty cannot bring about the formation of a legally binding agreement unless it is, ‘expressed’ in some external form.
(b) The Means of Expression of Consent to be Bound
42 According to Art. 11 VCLT, the ‘consent of a State to be bound by a treaty may be expressed by signature, exchange of instruments constituting a treaty, ratification, acceptance, approval or accession, or by any other means if so agreed’. There are no strict rules on the manner in which consent to be bound may be expressed; parties to a treaty may decide this between themselves, the matter generally being specified in the treaty itself.
43 Art. 2(1)(b) VCLT provides that ‘“ratification”, “acceptance”, “approval” and “accession” mean in each case the international act so named whereby a State establishes on the international plane its consent to be bound by a treaty’. In the case of ratification, it needs to be borne in mind this is not the internal process of ratification (in States with democratic constitutions, generally by way of act of the legislature), but an international act of the State, usually by way of signature by the Head of State or Government, or by a Foreign Minister, of a document in the form of an act of ratification.
44 There was a debate concerning the theoretical supremacy, in the absence of an agreement by the parties, of signature or ratification as the decisive means of expressing consent to be bound. This is not entirely settled, yet. In support of a requirement for ratification, in the absence of agreement to the contrary, it may be noted that in 1924, Judge Moore stated in Mavrommatis Palestine Concessions (Greece v Great Britain) (Jurisdiction) (Mavrommatis Concessions Cases) that the view that treaties might be regarded as binding before they had been ratified was obsolete (at 57).
45 Acceptance or approval of a treaty following signature, unless the treaty otherwise provides, fulfil the same function as ratification following signature, and follow similar rules (Art. 14(2) VCLT). The modes of expressing consent to be bound by acceptance and approval following signature were introduced into treaty practice in order to accommodate different internal or constitutional law procedures relating to the treaty-making process.
46 Accession (which is the act whereby a State accepts the offer or the opportunity to become a party to a treaty already negotiated and signed by other States) is regulated by Art. 15 VCLT according to which a State may accede to a treaty if it so provides, or if the parties agree.
(c) The Interim Stage between Signing and Ratification of a Treaty
47 The interim stage between the signing of a treaty and its ratification enables States to obtain any necessary parliamentary approval and/or to enact required legislation. Signature of a treaty in itself only expresses consent to be bound when it constitutes the final stage in the process of making a particular treaty.
48 With regard to the interim obligation not to defeat a treaty’s object and purpose prior to its entry into force (Treaties, Object and Purpose; Treaties, Provisional Application), codified in Art. 18 VCLT, reference may be made to what has been termed the US’s ‘unsigning’ of the Rome Statute of the International Criminal Court ([adopted 17 July 1998, entered into force 1 July 2002] 2187 UNTS 90 [‘Rome Statute’]) in 2002. This refers to the US’s letter informing the depository of the Rome Statute of the US’s intention not to become a party to the treaty. While no withdrawal of signature actually occurred, the interim obligation, to the extent that it exists under the customary international law of treaties, was terminated with regard to the US, who are not a party to the VCLT.
(d) Entry into Force
49 Entry into force means that the treaty becomes binding upon the parties to it and acquires full legal force as a legal act (Treaties, Conclusion and Entry into Force). Prior to the treaty’s entry into force, some of its final clauses are already applicable (those referred to in Art. 24(4) VCLT). Regarding multilateral treaties, a distinction can be made between the treaty’s general entry into force and its entry into force for a particular State. The treaty’s general entry into force occurs upon fulfilling the conditions prescribed in the treaty itself. After this general entry into force, the treaty may enter into force for a particular State once such a State has expressed its consent to be bound by the treaty.
50 Entry into force may be distinguished from entry into operation. Entry into force involves the commencement of the legal obligation of the parties to perform in accordance with the provisions of the treaty; entry into operation relates to the actual commencement of that performance.
51 Entry into force of a treaty may have legal effects within the domestic legal system of the States party to it. States Parties may be under an obligation to modify the national legal system so as to implement the international obligation. In principle, States have several options on how to achieve this objective. They may do so either by altering the national law or by incorporating the international agreement in question into their legal system. Occasionally international agreements prescribe which actions on the national level are to be undertaken. For example, Art. 4 International Convention on the Elimination of all Forms of Racial Discrimination ([opened for signature 7 March 1966, entered into force 4 January 1969] 660 UNTS 195) requires parties to suppress and punish the incitement to racial hatred by declaring such acts as criminal offences. Most multilateral environmental agreements require implementing national legislation or administrative actions. Instances of such action include the setting up of systems to implement at domestic level the emissions reductions required of developed States under the Kyoto Protocol, and the creation of civil liability regimes, for instance in relation to oil pollution and nuclear accidents.
5. Consent to be Bound through ‘Conferences’, or ‘Meetings’, of the Parties (COPs/MOPs)
52 A legally interesting phenomenon in recent years in relation to the question of consent to be bound is the growing ‘legislative’ powers of conferences of the parties or meetings of the parties (‘COPs’ or ‘MOPs’; Conference [Meeting] of States Parties) established by a number of modern multilateral treaties, including matters of the law of the sea, in the human rights field, treaties in the economic and health fields such as the WHO Framework Convention on Tobacco Control ([adopted 21 May 2003, entered into force 27 February 2005] 2302 UNTS 166), and some of the MEAs.
53 Some of these agreements set up organs such as the COPs/MOPs which are mandated to carry out certain functions in relation to the implementation and operation of the treaty regime. This may, but does not always, involve the use of so-called ‘enabling clauses’ which give a specific mandate to such organs to elaborate in more detail rules in particular areas without providing for specific amendment procedures.
54 One of the first examples of such provisions is the procedure for ‘adjustments and reductions of production or consumption of the controlled substances’ provided in Art. 2(9) 1987 Montreal Protocol. Another well-known example is the enabling clauses of the Kyoto Protocol (Arts 6, 12, 17) whereby the COP/MOP is mandated to elaborate the rules and procedures of the extremely important ‘flexible mechanisms’, including in particular the emissions trading system, which are only covered in a very general sense in the Kyoto Protocol itself.
55 Thus, States Parties to certain multilateral treaties, by comparison to the traditional expression of consent ex post facto (in relation to the content of the agreement) express their consent to be bound ‘in advance’ and without prior full knowledge the content of the agreement. It may be said that the precursor of such powers of the organs of international organizations can be found in the system of the tacit agreement or in other words, the opting out system (Tacit Consent/Opting Out Procedure). States have developed different mechanisms to nationally implement such ‘secondary rules’ developed by meetings of States Parties.
6. Treaties, Reservations
(a) Nature of Reservations
56 The VCLT provides the following definition in Art. 2(1)(d):
57 Broadly, reservations are a means whereby the parties to a treaty may, individually, modify the extent of their consent to the terms of the treaty. Generally, the issue of reservations is only relevant in the context of multilateral treaties (Treaties, Multilateral, Reservations to). The right to make reservations is part and parcel of a State’s expression of consent to be bound by the treaty, in the sense that it should only be bound by precisely that to which it has consented. The corollary of this is that other States cannot be obliged, against their will, to accept the reservation. It follows that in relation to a multilateral treaty, where one or more parties make a reservation which some parties accept and others do not, the effect of the reservations system is to give rise to a series of differentiated obligations as between pairs of parties. In other words, reservations to a certain extent ‘bilateralize’ the relations under a multilateral treaty.
(b) The Regime of the Vienna Convention
59 The VCLT reservations regime is characterized by its attempt to strike a balance between ‘integrity’ and ‘universality’, by which is meant the integrity (of the content) of a treaty and the widest possible participation. Art. 19(c) VCLT aims at preserving the integrity of the core of the treaty’s content in providing that a State may not submit a reservation, which is ‘incompatible with the object and purpose of the treaty’. Art. 20(4)(b) VCLT tips the balance towards widening participation by providing for treaty relations even between a reserving and an objecting State, unless a contrary intention is expressed by the objecting State. Art. 20(5) VCLT provides that, in general, a reservation is considered to have been accepted if it is not objected to within 12 months of its notification. Finally, while reservations to treaty provisions which codify customary international law are possible, reservations to provisions reflecting norms of ius cogens are not.
60 There are several unresolved issues in respect to reservations. First, the method for determining the object and purpose of a treaty is far from uncontroversial. Secondly, the legal consequences of a reservation being ‘impermissible’ due to its incompatibility with the treaty’s object and purpose are contested. DW Bowett coined the terminology for the two schools of thought which have emerged with regard to this problem: according to the school of ‘opposability’ (famous proponent eg JM Ruda), the permissibility of a reservation depends exclusively on its acceptance by another State (it is suggested that its compatibility with the treaty’s object and purpose could serve as a guideline for the State’s decision on whether or not to accept it); according to the school of ‘impermissibility’ (famous proponent eg DW Bowett), a reservation is invalid from its inception if it is impermissible due to its incompatibility with the treaty’s object and purpose, and the acceptance by other parties will not repair it. In other words, only permissible reservations can, in a second step, be accepted or, for other reasons than incompatibility with the treaty’s object and purpose, be objected to. The question of so-called impermissible reservations resulted in a discussion on the severability of such reservations from the State’s expression of consent. This problem is particularly pertinent in relation to reservations to human rights treaties (see eg the jurisprudence of the European Court of Human Rights [ECtHR] in relation to reservations to the European Convention for the Protection of Human Rights and Fundamental Freedoms [(signed 4 November 1950, entered into force 3 September 1953) 213 UNTS 221]).
(c) Further Developments
61 In 1993 the unresolved issues in the reservations regime of the VCLT prompted the ILC to undertake a topic entitled ‘The Law and Practice Relating to Reservations to Treaties’, on which Professor A Pellet was appointed as Special Rapporteur. Six major problems of substance predominated in the discussion within the ILC that followed Pellet’s first report: the definition of reservations; the distinction between them and interpretative declarations (see para. 62below), and the differences of their legal regime which characterize the two legal institutions; the doctrinal dispute between the ‘permissibility’ and ‘opposability’ schools; the settlement of disputes; the effects of succession of States on reservations; and the question of the unity or diversity of the legal regime applicable to reservations.
(d) Interpretative Declarations
62 States may also append ‘interpretative declarations’ to treaties when expressing their consent to be bound (Treaties, Declarations of Interpretation). Such declarations are not addressed in the VCLT. As opposed to reservations, mere interpretative declarations are explanatory in character and set out how a State perceives its treaty obligations. In practice it may be difficult to draw the line between ‘mere interpretative declarations’ and ‘reservations’. In the event that so-called interpretative declarations aim at changing the scope of the obligation, they cease to be declarations and become reservations, as a result of which States may treat them as reservations (so-called ‘qualified interpretative reservations’) (see eg Belilos v Switzerland [ECtHR] Series A No 132).
7. Invalidity of Treaties
(a) The Right to Impeach the Validity of a Treaty
63 According to Art. 42(1) VCLT the validity of a treaty or of the consent of a State to be bound by a treaty may be impeached only through the application of the VCLT (Treaties, Validity). The invalidity or termination in whatever form of a treaty under the VCLT itself does not impair the duty of any State to fulfil any obligations embodied in the treaty to which it would be subject under international law independently of the treaty (Art. 43 VCLT; Treaties, Termination). A State may lose a right to invoke a ground for invalidating or terminating a treaty if, after becoming aware of the facts, it asserts or acquiesces in the treaty’s validity either by express agreement or through its conduct (Art. 45 VCLT).
(b) Grounds for Invalidity
64 Generally, the grounds for invalidity of treaties within the VCLT can be divided into two groups: relative grounds in Arts 46 to 50; and absolute grounds in Arts 51 to 53. The main difference between these grounds is that the establishment of an absolute ground means that the treaty has no legal force, whilst the establishment of a relative ground means that the consent of a particular State to a multilateral treaty is invalidated (Art. 69(4) VCLT). This will not cause the treaty as a whole to be void and the treaty will remain valid as between the remaining parties. However, the treaty relations between the State whose consent has been invalidated and the other States are void. With regard to bilateral treaties, the establishment of relative and absolute grounds have an identical effect, they both render the treaty void.
65 Art. 46 VCLT deals with the failure to comply with internal law regarding competence to conclude a treaty, and provides that this may be a ground for invalidating the treaty, if that failure was ‘manifest’. Art. 47 VCLT concerns the situation in which the representative purporting to conclude the treaty were acting ultra vires. Art. 48 VCLT addresses the effect of error in relation to consent to be bound by a treaty (see the 1962 Temple of Preah Vihear Case). Arts 49 and 50 VCLT deal with fraud and corruption. The coercion of a representative (Art. 51 VCLT) and coercion of a State (Art. 52 VCLT) and conflict with the norm ius cogens (Art. 53 VCLT) are absolute grounds for invalidity of a treaty. The consequences of such invalidity are regulated by Art. 71 VCLT.
(c) International Law’s Tendency in Favour of Stability and Validity
66 As a general proposition, it can be said that international law favours the stability of treaty relations, for instance see Art. 62 VCLT. Thus the ICJ in the 1997 Gabčíkovo-Nagymaros Case (Hungary/Slovakia) observed that the stability of treaty relations implies that the plea of fundamental change of circumstances should be applied only in exceptional circumstances (at 65; Treaties, Fundamental Change of Circumstances).
67 In the same case the ICJ took the view that the violation of treaty rules or of rules of general international law may justify the adoption of certain measures, including countermeasures by an injured State but it does not constitute a ground for termination under the law of treaties (ibid 65).
8. Treaties, Revision, Amendment, and Modification
68 In the VCLT, the term ‘amendment’ refers to changes to the treaty as between all the parties, whereas ‘modification’ relates to changes between certain of the parties only (inter se), a distinction which is only relevant in the context of multilateral treaties (Arts. 39–41; Treaties, Amendment and Revision). The VCLT does not use the term ‘revision’ of treaties, based on the ILC’s perception that certain ‘nuances’ had become attached to it in the period preceding World War II (Commentary to Art. 35, UN ILC ‘Draft Articles on the Law of Treaties with Commentaries’  GAOR 21st Session Supp 9, 20). Nevertheless, the term is still used in practice, and the distinction between the procedures of ‘amendment’ and ‘revision’ is not clear-cut. Broadly, two views can be distinguished in the practice of the law of treaties. According to one, revision basically means amendment. According to the other, revision is a more comprehensive process resulting in changes to the treaty as a whole, as opposed to changes to specific provisions of a treaty. Support for this view can be found in treaties which regulate both their amendment as well as their revision, such as the UN Charter (Arts 108, 109 respectively), or the 1974 Convention on the Protection of the Marine Environment of the Baltic Sea (Arts 23, 22 respectively), but, as indicated above, this use of terms is not consistent in State practice.
69 The default rule in the VCLT provides that a treaty can be amended by agreement between the ‘parties’. Art. 2(1)(g) VCLT implies that the treaty, which is to be amended, has already entered into force. In practice, however, there are examples of treaties which have been amended prior to their entry into force. The most famous example of these is probably the United Nations Convention on the Law of the Sea ([concluded 10 December 1982, entered into force 16 November 1994] 1833 UNTS 397), Part XI of which was not only ‘implemented’ but in effect amended by the so-called ‘1994 Implementation Agreement’ (Agreement Relating to the Implementation of Part XI of the United Nations Convention on the Law of the Sea of 10 December 1982 [done 28 July 1994, entered into force 28 July 1996] 1836 UNTS 41; Implementation Agreements).
70 Furthermore, a treaty may be amended through the subsequent and uniform practice of all its parties. A well-known example of this relates to Art. 27(3) UN Charter, which concerns voting in the UN Security Council. Despite the terminology of an ‘affirmative vote of nine members including the concurring votes of the permanent members’, a subsequent practice has developed according to which the abstention of a permanent member, which must be distinguished from a negative vote (Veto), does not prevent the adoption of a resolution. In the ICJ advisory opinion Legal Consequences for States of the Continued Presence of South Africa in Namibia (South West Africa) notwithstanding Security Council Resolution 276 (1970) (Advisory Opinion) (‘Legal Consequences of South Africa in Namibia’), the ICJ noted that this practice had been generally accepted by the Member States of the UN.
F. Treaties, Interpretation
1. General Principles
85 Treaty interpretation is to some extent regulated by the VCLT, nevertheless, many problems remain controversial.
86 A fundamental set of principles of interpretation of treaties was proposed by Sir G Fitzmaurice, who based it on the practice of the ICJ. These are as follows: Principle I: of actuality—that treaties have to be interpreted as they stand, on the basis of their actual text. Principle II: the natural and ordinary meaning—that subject to the principle of contemporaneity (where applicable), particular words and phrases are to be given their normal, natural, and unrestrained meaning in the context in which they occur. This principle can only be displaced by direct evidence that the terms used are to be understood in a manner different to their natural and ordinary meaning, or if such an interpretation would lead to an unreasonable or absurd result. Principle III: integration—that treaties are to be interpreted as a whole. This principle is of fundamental importance and means that individual parts, chapters, or sections of a treaty are not to be interpreted out of their overall context. The remaining principles take effect subject to the three principles outlined above. These are: Principle IV: effectiveness (ut magis valeat quam pereat)—that treaties are to be interpreted with reference to their declared or apparent objects and purposes; and particular provisions are to be interpreted so as to give them the fullest effect consistent with the normal sense of the words and with the text in such a way that a reason and meaning can be attributed to every part of the text. Principle V: subsequent practice—that recourse may be had to subsequent practice of parties relating to the treaty. Principle VI: contemporaneity—that the terms of a treaty must be interpreted in the light of linguistic usage current at the time when the treaty was concluded.
2. Three Schools
87 In general there may be said to exist three general schools of, or approaches to, interpretation: the subjective (the ‘intention’ of the parties) approach; the objective (the ‘textual’) approach; and the teleological (the ‘object and purpose’) approach. These three schools of interpretation are not mutually exclusive and the VCLT draws on all three. However, it is debatable whether the VCLT successfully combined the objective and subjective approaches, which in the view of many appear to be effectively irreconcilable. The ILC adopted the ‘textual’, rather than the ‘intention of the parties’ approach, on the basis that it is to be presumed that the text represents the real expression of what the parties in fact intended.
88 The ICJ has consistently adhered to the textual interpretation as being the most important, as in the Territorial Dispute Case (Libyan Arab Jamahiriya/Chad), where it stated as follows: ‘Interpretation must be based above all upon the text of the treaty. As a supplementary measure recourse may be had to means of interpretation such as the preparatory work’ (at 22). The determination of the ordinary meaning of the term is undertaken in the context of the treaty as a whole and in the light of its object and purpose (see eg Interpretation of the Convention of 1919 Concerning Employment of Women during the Night [Advisory Opinion] PCIJ Series A/B No 50).
89 In many cases, the ICJ has stated that, ‘in accordance with customary international law, reflected in Article 31 of the VCLT, a treaty must be interpreted in good faith in accordance with the ordinary meaning to be given to its terms in their context and in the light of its object and purpose’ (see eg the 1994 [Territorial Dispute Case [Libyan Arab Jamahiriya/Chad] at 19–20; Good Faith [Bona fide]). The underlying principle is that the treaty is to be interpreted in good faith, which is the embodiment of the principle pacta sunt servanda.
3. Object and Purpose
90 According to the general rule on interpretation in Art. 31(1), a treaty shall also be interpreted in the light of its object and purpose. As already mentioned in the context of reservations, considerable uncertainty surrounds the determination of a treaty’s object and purpose. Despite frequent references to the criterion, the jurisprudence of several international courts and tribunals (including the Permanent Court of International Justice [PCIJ], the ICJ, and others) has not clarified the existing ambiguities. In academic writing, it is contested whether the terms ‘object and purpose’ are synonymous (English and German writers) or not (French writers). According to the latter view, ‘object’ refers to the content of the treaty, while ‘purpose’ designates the overall aim to be achieved by means of the treaty. Furthermore, the methodology for establishing a treaty’s object and purpose is far from clear. In the jurisprudence, recourse has been had, inter alia, to the following criteria, individually or cumulatively: the title of the treaty; its preamble; an article of the treaty with apparent relevance for the treaty’s object and purpose; and the travaux préparatoires; etc.
4. Place of Subsequent Practice
91 Another problem concerns what is to count as constituting subsequent practice for the purposes of interpretation, the use of which is sanctioned as forming part of the context of the treaty by Art. 31(3) VCLT. In the 1999 Kasikili/Sedudu Island Case (Botswana/Namibia), the ICJ adhered to the view that the subsequent practice of parties to a treaty constitutes an element to be taken into account when determining its meaning, but it adopted a restrictive approach to what comprises subsequent practice and did not take into account unilateral acts of the previous authorities of Botswana on the grounds that these were for internal purposes only and unknown to the Namibian authorities.
5. Place of Traveaux Préparatoires
92 One of the most controversial issues in treaty interpretation is the use of travaux préparatoires (preparatory work). The VCLT gives very specific conditions under which travaux préparatoires may be used: either to confirm the meaning of the treaty or as an aid to interpretation where, following the application of Art. 31 VCLT, the meaning is obscure or leads to a result which is manifestly absurd or unreasonable. The ICJ has always made very restrictive use of travaux préparatoires. This approach, however, has given rise to the view that the ICJ has not always established sufficiently the requisite common intention of the parties (see the 1995 Maritime Delimitation and Territorial Questions between Qatar and Bahrain [Qatar v Bahrain] [Dissenting Opinion of Vice-President Schwebel]; Case between Qatar and Bahrain ).
6. Principle of Effectiveness
93 The principle of effectiveness in treaty interpretation is closely related to the notion of the ‘object and purpose’ of the treaty. This is, however, a very ill-defined term, making it an unreliable tool for interpretation. The principle of effectiveness is enshrined in the maxim: magis valeat quam pereat. Although this principle can operate as an element within the object and purpose principle, it is not limited to this role. The ICJ has used it to ascertain the intention underlying a treaty and as a broader point for discussion.
G. Effect of Treaties on Third Parties
1. The General Rule
97 The fundamental principle relating to the effect of treaties on third States is contained in the maxim pacta tertiis nec nocent nec prosunt, which means that treaties have no legal effect on third States (Treaties, Third-Party Effect). Treaties are res inter alios acta for these States. This main rule is embodied in Art. 34 VCLT: ‘[a] treaty does not create either obligations or rights for a third State without its consent’.
2. Treaties Providing for Rights and Obligations for Third States, and Treaty Rules Becoming Binding on Third States through International Custom
98 Art. 35 VCLT codifies the rule on treaties providing for obligations for third States. An obligation may arise from a treaty for third States if two conditions are fulfilled: the parties to the treaty intended the provision to be the means of establishing the obligation and the third State expressly accepts the obligation in writing. However, the possibility of concluding a treaty imposing obligations on third States, even on the basis of the above-mentioned conditions, is not without controversy.
99 Rights derive from a provision of a treaty for a third State, if the parties so intended and the third State assents thereto (Art. 36 VCLT). Assent may be presumed ‘so long as the contrary is not indicated, unless the treaty otherwise provides’ (Art. 36 VCLT). Possibly, one of the examples of such a situation would be the most-favoured-nation clause.
100 Finally, a rule set out in a treaty may be (or become) binding on third States as a rule of customary international law (Art. 38 VCLT). In the 1969 North Sea Continental Shelf Cases, the ICJ described different ways in which treaties and customary international law may interact, and recognized the possibility of the existence of identical rules in international treaty law and customary international law. (On this last point, see also the Nicaragua Case 95–6).
3. Objective Regimes
101 One of the unresolved and controversial issues, which is not included in the VCLT, remains the problem of treaties establishing so-called objective regime[s], ie regimes which are opposable to all States. Examples of such treaties are those establishing the demilitarized zones (Demilitarization). There is also the view that the legal regime on Antarctica is an objective regime (see eg E Klein Statusverträge im Völkerrecht: Rechtsfragen Territorialer Sonderregime [Springer Berlin 1980]).
126 The law of treaties constitutes one of the three pillars of international law together with sources of international law and the law of State responsibility. Treaties are the most commonly used means of creating binding norms between sovereign States. Some of the areas of international law are almost exclusively regulated by treaties, such as international environmental law, in which customary international law plays a minor role. The relationship between treaties and customary international law is of fundamental importance, in particular in cases of multilateral treaties, which are intended to give rise to a norm of customary international law, a process which has to be treated with great caution.
127 The basic principle of the law of treaties, pacta sunt servanda, remains the fundament on which the whole of the system of treaty obligations is built. The most authoritative source of the rules concerning the law of treaties is the VCLT, in most parts representing existing customary international law. However, some issues remain unresolved, such as the question of reservations, in particular reservations to human rights treaties, a problem which is at present on the agenda of the ILC. Some questions are not within the remit of the VCLT, such as unequal treaties or the effect of armed conflict on the law of treaties, which remains one of the unresolved issues and therefore currently also under the consideration of the ILC. There are other problems which present difficulties, such as the relationship between the material breach of a treaty and the international law of countermeasures, as well as the role of travaux préparatoires in the interpretation of treaties. The question of the succession to treaties is not fully resolved either, and it is common ground between States that the VCSS-T only in part codifies existing customary international law.
128 Many points of the law of treaties are still being clarified and crystallized by international courts and arbitral tribunals, in particular the ICJ, as well as by the monitoring bodies established on the basis of multilateral human rights agreements, in areas such as the reservation to treaties, the rule of treaty interpretation, the termination and invalidity of treaties, and the relationship between the rules of the law of treaties and those of State responsibility. Some treaties are living instruments and therefore their application by courts and tribunals, as well as States’ practice, contributes to their further development and a better understanding of how they work. Further, the contribution of international organizations to the development of treaties must be noted, as well as that of the European Union, specifically the unique way in which it created a particular system of treaties (European Community, Mixed Agreements). The EU applies the law of treaties and the VCLT, and therefore participates in its interpretation and elaboration.
129 It also must be observed that the work of the ILC in other areas than the law of treaties also contributes to its development and crystallization, for instance in relation to the topic of ‘Fragmentation of International Law: Difficulties Arising from the Diversification and Expansion of International Law’, in which the ILC analyses Arts 31(3)(c), 30 (application of successive treaties relating to the same subject-matter), and 41 VCLT.
130 International treaties now fulfil a very wide range of purposes, in particular providing at the international level many of the functions fulfilled by acts of parliament or other legislation at the municipal level. Treaties and binding decisions of international organizations are the vehicle whereby States can deliberately make rules or dispositions among themselves which are binding in international law. Contemporary international relations are characterized by the expansion of treaties, in particular in areas such as international environmental law, international economic law, international law of the sea, and international criminal law.
131 Moreover, there are several features of the treaty-making process which may put in doubt the appropriateness of treaties as the main tool for regulating international relations. The conclusion and entry into force of international treaties may be a lengthy procedure making it difficult to respond quickly to new challenges. Striving for the universality of a treaty may result in allowing reservations which in turn further weaken the effectiveness of the treaty. Considering the increase of international treaties and their growing impact on national law, their legitimacy has been called into doubt. One may wonder whether the cure—if a cure is needed at all—may rest in national rather than international law. The law of treaties itself addresses the problem of the possibly lengthy treaty-making procedure by providing for the provisional application of treaties under Art. 25 VCLT.
132 Since treaties only bind the participating parties, it is difficult to effectively regulate issues considered to be of global concern, such as climate change.
133 States have tried to overcome the inherent deficiencies of the treaty-making procedure or treaties themselves by devising ways to make treaties reflect more accurately the political, economic, and social realities, and to respond to scientific progress or other changes in general. Examples of such devices may be found, for example, in international environmental law, where States developed new mechanisms of expressing consent to be bound, thereby making those treaties more flexible. This, however, in turn may lead to questions regarding the legitimacy of norm-making power by organs created by multilateral environmental treaties. Framework agreements reflect the phenomenon that sometimes only an agreement on general principles was reached. Such framework agreements may later be supplemented by additional protocols or implementation agreements negotiated sometimes in conferences reflecting a particular expertise.