The analytical requirements of Moore in ethical questions are so high that we labour under the impression that all morals and ethics before (and even after) he wrote the Principia, fall into the delusion he calls "naturalistic". It may be granted that to do one’s duty, to realize one’s person, to follow a particular intuition etc.. is to do good ; but why would the good consist in doing one’s duty, realizing one’s person and conforming to a particular affect ? It is difficult to see how Utilitarianism would allow to resolve the "inverse problem" ; yet Moore claims himself to be a Utilitarian and inscribes his purpose in the wake of Bentham’s, Stuart Mill’s and Sidgwick’s. How is it possible? Of course, there are many sorts of Utilitarianism. What did Moore want? Did he want, at the beginning of the twentieth century, to add another sort of utilitarianism to a long list of ramifications and branching? What meaning should we give his ideal utilitarianism, as he called and promoted it in Principia Ethica?