Subsequent Agreements and Subsequent Practice within and Outside the Vienna Convention

The wording of art 31(3)(a) is very clear, and is dedicated to a circumstance (a subsequent agreement explicitly interpretive of the previous one) that does not create any confusion. In dealing with subsequent practice, however, things are much more complicated. It is reductive to assert that the only possible use of subsequent practice falls under art 31(3)(b). Case law shows us that subsequent conduct has broader interpretive potential: not only when the practice culminates in an agreement; not only when the practice originates in the application of the treaty; not only when the practice is that of the parties.