Focusing on some undertheorized aspects of Article 31(3)(c) of the Vienna Convention on the Law of Treaties, the present article aims to reassess critically the anti-fragmentation function generally assigned to this provision. The high hopes associated with the harmonizing potential of Article 31(3)(c) are usually based on a reading of this provision as requiring the interpreter to take into account not only rules applicable between all of the parties to the treaty, but also those applicable only between some of the parties. However, this reading does not seem to be confirmed by the interpretive approach suggested in this article. On the other hand, the use of Article 31(3)(c) in judicial settings raises a structural problem inherent in the international judiciary. The analysis undertaken along these lines suggests that the optimism that Article 31(3)(c) has recently provoked should be qualified in some important respects.
