In a previous paper it was argued that neither the tacit consent theory nor the opinio juris theory were by themselves capable of explaining the nature of customary international law, although each of them does indeed stress an important aspect—the tacit consent theory that custom is a lawmaking process, and the opinio juris theory that there must be some difference between customary law and practices which do not express, or do not give rise to law. What has to be done is to reformulate these approaches in such a way as to preserve the insights of each, while avoiding their errors.
A good starting point is the older tacit consent theories of the Civilians and Canonists, which were described in the previous paper. Their approach has the following characteristics:
i) By “consent” they mean, not contractual consent, but simply the intention to create law; therefore—
ii) they are able to admit that custom can bind individuals that have no part in its creation, even without their consent;
iii) they consider that the rules of customary law are binding absolutely, and not merely on a reciprocal basis; and
iv) finally, these jurists show an awareness of the fact that the conditions which regulate the formation of customary law are themselves rules of law, rather than necessary truths that can be deduced from the nature of custom.