Opposability and Non-Opposability in International Law

In a given legal situation relating to one or more states, the most practically important question to be determined is not whether, in an objective sense, a legal act is or is not generally valid. It is instead whether, as far as the relationship between the states involved is concerned, the act is opposable by one state to another. Opposability is the capacity of a rule, a legal act, a right, or a legal fact to produce international legal effects vis-à-vis a state, including a state or states unconcerned by the obligations that arise directly from it. Rather than depending on whether an act is valid as against all the world, opposability operates in the relations between pairs of states. Opposability (like its opposite: non-opposability) is concerned with whether the act in question may be opposed to the state at issue; the basis for that opposability (or non-opposability) will be whether or not the state has given its recognition, tacitly or explicitly, of the act concerned.