Kelsen wrote a book, much less known than his Reine Rechtslehre (Pure Theory of Law), called Was ist Gerechtigkeit (What is Justice), in which he attempts to show how and why several theories of justice, formulated by authors ranging from Greece to European Illuminism, are wrong. One of those concepts is Aristotle’s, as exposed in his Nichomachean Ethics. In this article, I argue that in order to show Aristotle wrong, Kelsen misinterprets his theory, then ignores the practical consequences it implies. I attempt to demonstrate that, although highly influenced by the (retrograde) mores of his time, Aristotle’s theory can be useful to us today, which Kelsen denies. Finally, I present a challenge regarding one point raised by Kelsen which is particularly hard to reply.