The foregoing is obviously not ground-breaking. I nonetheless appreciate that reducing ILP to a theory of ascertainment remains quite problematic to a number of people. To classical positivists, for instance, this is a betrayal of the quest for legal certainty toward
which ILP should, in their view, be entirely geared. To Kelsenian scholars, such an approach is not different from naturalism and condemns international lawyers to be sociologists. To Dworkinians, Hart’s idea that lawyers must share the same law ascertainment tests makes
disagreement between law-applying authorities impossible, because an agreement about the law ascertainment tests involves agreement about their correct application (this is the so called semantic sting argument). Eventually, to legal realists and critical legal scholars, Hartian reductionist positivism is naïve, because even if grounded in social practice, the theory of sources it relies on is bound to fall into the trap of objectivism, as there is inevitably a need for a ‘‘value fact’’ to capture the practice of law-applying authorities. Some of these objections are surely weighty and must be assumed. Indeed, the reductionism advocated here makes ILP an extremely modest approach. It is also true that it presupposes some empiricism, which can never be seen as objective and necessarily relies on some ‘‘value fact.’’ Such an
empiricism is inherent in the social foundation of law and is precisely what allows the theory of sources to be made dynamic. If this condemns international lawyers to be sociologists, so be it.