The paper demonstrates that Parmenides’ monism is a logical consequence of his criteria for philosophy, in conjunction with the logical operators he uses, and their holistic connection. Parmenides, I argue, is the first philosopher to set out explicit criteria for philosophy, establishing as criterion not only consistency, but also what I call rational admissibility, the requirement when giving an account of something that the account be based on rational analysis and can withstand rational scrutiny. I give a detailed account of (...) the logical operators Parmenides uses in his argument and of the way in which his notion of being is tailored to fit both them and his criteria for philoso-phy. (shrink)