Check out The ICJ and Evolutionary Treaty Interpretation by Marko Milanovic on EJIL:Talk!. Here is a taste:
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[T]o sum up: because the contracting parties used a generic term, commerce, and created a perpetual regime, the meaning of the term ‘commerce’ is to be updated every time that the treaty is applied. It is its 2009, not its 1858, meaning that governs.
This approach of the Court is of course quite familiar - it is used all the time in many domestic legal systems in interpreting constitutional provisions, as well as in international human rights law. Cf. the European Court’s view of the ECHR as a ‘living instrument,’ etc., etc. Indeed, a problem closely analogous to this one is the US Supreme Court’s interpretation of the Commerce Clause of the US Constitution, giving Congress the power to regulate foreign and inter-state commerce. But this method of evolutionary interpretation is, of course, controversial, especially in the US, with the various incarnations of the originalist movement arguing that the Constitution should be interpreted in accord with the original intentions of its framers, or (as is now the case) in accord with its original public meaning.
