This article examines the reasoning and findings of the International Court of Justice in its judgment in Costa Rica v. Nicaragua on issues relating to the effect of the passage of time on the interpretation of treaties. In arriving at the proper interpretation of the disputed phrase ‘for purposes of commerce’ in a Treaty of Limits between the parties, which entered into force in 1858, the ICJ followed a number of interpretative steps based on Article 31 of the Vienna Convention on the Law of Treaties (VCLT), which led the Court to conclude that the meaning of this phrase must be presumed to have evolved over time. The means and methods of interpretation employed by the ICJ to determine the effect of the passage of time on treaties are examined. More specifically, the question is raised whether the ICJ's approach to determining the evolutionary character of a treaty provision, based on an interpretative presumption, may not be considered unsatisfactory insofar as it does not appear to take full account of the actual common intention of the parties – the main task of interpretation.
