Hans Kelsen’s purity thesis is the basic methodological principle of the Pure Theory of Law. Indeed, it is no exaggeration to say that virtually everything that is peculiar to Kelsen’s legal theory stems from the purity thesis. This includes Kelsen’s normativism or non‐naturalism and his polemic against various dualisms in legal science. I set out Kelsen’s position on these issues after looking at the nomenclature of purity in his writings as well as the philosophical and contextual sources of purity as (...) he understands them. (shrink)