Pacta sunt servanda

Pacta sunt servanda means agreements must be kept. It is the foundation of the law of treaties. Article 26 of the Vienna Convention on the Law of Treaties, 1969, headed pacta sunt servanda, provides that every treaty in force is binding upon the parties to it and must be performed by them in good faith. Article 27 adds that a party may not invoke the provisions of its internal law as justification for its failure to perform a treaty.

The rule has two parts: the treaty binds, and it must be performed in good faith. Good faith forbids a party from defeating the object and purpose of the treaty by technical or evasive conduct. The rule applies only to a treaty in force, so a treaty that is invalid or has been terminated does not bind. Its main exception is rebus sic stantibus, the doctrine of fundamental change of circumstances in Article 62 of the Vienna Convention, which allows termination or withdrawal only in narrow conditions and not for a boundary treaty.

India is not a party to the Vienna Convention, but the rule in Article 26 is accepted as customary international law. Article 51(c) of the Constitution, a Directive Principle, directs the State to endeavour to foster respect for international law and treaty obligations. Article 253 empowers Parliament to make any law for implementing a treaty, agreement or convention with other countries. Because India follows a dualist approach, a treaty that affects the rights of citizens or requires a change in domestic law needs legislation before courts enforce it, though courts read domestic law in harmony with India's obligations where they can.

In private law the same idea underlies the binding force of contracts. Section 37 of the Contract Act requires parties to perform, or offer to perform, their respective promises unless performance is dispensed with or excused by law.