Conflicts between successive norms

(24) Lex posterior derogat legi priori. According to article 30 VCLT, when all the

parties to a treaty are also parties to an earlier treaty on the same subject, and the earlier

treaty is not suspended or terminated, then it applies only to the extent its provisions are

compatible with those of the later treaty. This is an expression of the principle according

to which “later law supersedes earlier law”.

(25) Limits of the “lex posterior” principle. The applicability of the lex posterior

principle is, however, limited. It cannot, for example, be automatically extended to the

case where the parties to the subsequent treaty are not identical to the parties of the

earlier treaty. In such cases, as provided in article 30 (4) VCLT, the State that is party

to two incompatible treaties is bound vis-a-vis both of its treaty parties separately. In

case it cannot fulfil its obligations under both treaties, it risks being responsible for the

21 See Legal Consequences for States of the Continued Presence of South Africa in Namibia

(South-West Africa) notwithstanding Security Council Resolution 276 (1970), Advisory Opinion,

I.C.J. Reports 1971, p. 16 at p. 31, para. 53. The Court said that the concept of “sacred trust”

was by definition evolutionary. “The parties to the Covenant must consequently be deemed to

have accepted [it] as such. That it is why, viewing the institutions of 1919, the Court must take

into consideration the changes which have occurred in the supervening half a century, and its

interpretation cannot remain unaffected by the subsequent development of law, through the

Charter of the United Nations and by way of customary international law. Moreover, an

international instrument has to be interpreted and applied within the framework of the entire

legal system prevailing at the time of interpretation.”

In the Case concerning the Gabč ikovo-Nagymaros Project (Hungary/Slovakia)

I.C.J. Reports 1997, pp. 76-80, paras. 132-147, the ICJ noted that: “[T]he Court wishes to point

out that newly developed norms of environmental law are relevant for the implementation of the

Treaty and that the parties could, by agreement, incorporate them … [in] … the Treaty. These

articles do not contain specific obligations of performance but require the parties, in carrying out

their obligations to ensure that the quality of water in the Danube is not impaired and that nature

is protected, to take new environmental norms into consideration when agreeing upon the means

to be specified in the Joint Contractual Plan …”.

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breach of one of them unless the concerned parties agree otherwise. In such case, also

article 60 VCLT may become applicable. The question which of the incompatible

treaties should be implemented and the breach of which should attract State responsibility

cannot be answered by a general rule. 22 Conclusions (26)-(27) below lay out

considerations that might then be taken into account.

(26) The distinction between treaty provisions that belong to the same “regime” and

provisions in different “regimes”. The lex posterior principle is at its strongest in regard

to conflicting or overlapping provisions that are part of treaties that are institutionally

linked or otherwise intended to advance similar objectives (i.e. form part of the same

regime). In case of conflicts or overlaps between treaties in different regimes, the

question of which of them is later in time would not necessarily express any presumption

of priority between them. Instead, States bound by the treaty obligations should try to

implement them as far as possible with the view of mutual accommodation and in

accordance with the principle of harmonization. However, the substantive rights of treaty

parties or third party beneficiaries should not be undermined.

(27) Particular types of treaties or treaty provisions. The lex posterior presumption

may not apply where the parties have intended otherwise, which may be inferred from the

nature of the provisions or the relevant instruments, or from their object and purpose.

The limitations that apply in respect of the lex specialis presumption in conclusion (10)

may also be relevant with respect to the lex posterior.

22 There is not much case-law on conflicts between successive norms. However, the situation

of a treaty conflict arose in Slivenko and others v. Latvia (Decision as to the admissibility

of 23 January 2002) ECHR 2002-II, pp. 482-483, paras. 60-61, in which the European Court of

Human Rights held that a prior bilateral treaty between Latvia and Russia could not be invoked

to limit the application of the European Convention on Human Rights and Fundamental

Freedoms: “It follows from the text of Article 57 (1) of the [European Convention on Human

Rights], read in conjunction with Article 1, that ratification of the Convention by a State

presupposes that any law then in force in its territory should be in conformity with the

Convention … In the Court’s opinion, the same principles must apply as regards any provisions

of international treaties which a Contracting State has concluded prior to the ratification of the

Convention and which might be at variance with certain of its provisions.”

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(28) Settlement of disputes within and across regimes. Disputes between States

involving conflicting treaty provisions should be normally resolved by negotiation

between parties to the relevant treaties. However, when no negotiated solution is

available, recourse ought to be had, where appropriate, to other available means of

dispute settlement. When the conflict concerns provisions within a single regime

(as defined in conclusion (26) above), then its resolution may be appropriate in the

regime-specific mechanism. However, when the conflict concerns provisions in treaties

that are not part of the same regime, special attention should be given to the

independence of the means of settlement chosen.

(29) Inter se agreements. The case of agreements to modify multilateral treaties by

certain of the parties only (inter se agreements) is covered by article 41 VCLT. Such

agreements are an often used technique for the more effective implementation of the

original treaty between a limited number of treaty parties that are willing to take more

effective or more far-reaching measures for the realization of the object and purpose of

the original treaty. Inter se agreements may be concluded if this is provided for by the

original treaty or it is not specifically prohibited and the agreement: “(i) does not affect

the enjoyment by the other parties of their rights under the treaty or the performance

of their obligations; (ii) does not relate to a provision, derogation from which is

incompatible with the effective execution of the object and purpose of the treaty as a

whole” (art. 41 (1) (b) VCLT).

(30) Conflict clauses. When States enter into a treaty that might conflict with other

treaties, they should aim to settle the relationship between such treaties by adopting

appropriate conflict clauses. When adopting such clauses, it should be borne in mind

that:

(a) They may not affect the rights of third parties;

(b) They should be as clear and specific as possible. In particular, they should

be directed to specific provisions of the treaty and they should not undermine the object

and purpose of the treaty;

(c) They should, as appropriate, be linked with means of dispute settlement.

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6. Hierarchy in international law: Jus cogens, Obligations erga omnes,