Articles 20–27

Articles 20–27 form the core operative provisions of the Vienna Convention on the Law of Treaties (VCLT), concluded at Vienna on 23 May 1969 and in force since 27 January 1980. Articles 19–23 codify the law of reservations — a State's unilateral statement purporting to exclude or modify the legal effect of certain treaty provisions in their application to that State (Article 2(1)(d)). Article 20 governs acceptance of and objection to reservations; Article 21 sets out their legal effects; Article 22 regulates withdrawal of reservations and objections; and Article 23 prescribes the procedure, requiring reservations and objections to be formulated in writing. This regime displaced the older "unanimity rule" in favour of the flexible system endorsed by the International Court of Justice in its Reservations to the Genocide Convention Advisory Opinion (1951), which introduced the object-and-purpose compatibility test now codified in Article 19(c).

Article 20 establishes that a reservation expressly authorised by a treaty needs no subsequent acceptance, while a reservation to a plurilateral treaty whose limited number of negotiating States indicates that the entire treaty must apply requires acceptance by all parties. In the ordinary case, acceptance by another contracting State makes the reserving State a party as between them, an objection does not preclude entry into force unless the objecting State definitely opposes it, and a reservation is deemed accepted if no objection is raised within twelve months. Article 21 then provides that a reservation modifies the relevant provisions reciprocally between the reserving State and accepting States to the extent of the reservation, but does not modify provisions inter se among other parties. Articles 24–25 cover entry into force and provisional application; Article 26 enshrines pacta sunt servanda — that every treaty in force binds the parties and must be performed in good faith — and Article 27 bars a party from invoking its internal law to justify failure to perform, subject to Article 46.

These provisions remain the governing framework in 2026, supplemented by the International Law Commission's 2011 Guide to Practice on Reservations to Treaties, which elaborated on impermissible reservations and the consequences of nullity. Human-rights treaty bodies, notably in the Human Rights Committee's General Comment No. 24 (1994), have argued for a distinct severability approach to invalid reservations under the ICCPR, generating ongoing doctrinal tension with the strict VCLT consent model. India is not a party to the VCLT but treats much of it, including Articles 26 and 27, as reflecting customary international law.

For the exam, Articles 20–27 are central to the International Law and Treaty Law segments of UPSC optional papers, FSOT, and CSS. Examiners commonly ask candidates to explain the compatibility test of Article 19(c), distinguish reservations from interpretative declarations, analyse the legal effects under Article 21, or apply pacta sunt servanda and Article 27 to a problem where a State pleads domestic law. A frequent question angle pairs the Genocide Reservations opinion (1951) with the VCLT codification to test understanding of how customary practice crystallised into treaty text.