              Aristotle’s commitment to essentialism runs deep.   He relies upon a host of loosely related locutions when discussing the essences of things, and these give some clue to his general orientation. Among the locutions one finds rendered as essence in contemporary translations of Aristotle into English are: (i) to ti esti (the what it is); (ii) to einai (being); (iii) ousia (being); (iv) hoper esti (precisely what something is) and, most importantly, (v) to ti ên einai (the what it was to be) (APo 83a7; Top. 141b35; Phys. 190a17, 201a18–21; Gen. et Corr. 319b4; DA 424a25, 429b10; Met. 1003b24, 1006a32, 1006b13; EN 1102a30, 1130a12–13). Among these, the last locution (v) requires explication both because it is the most peculiar and because it is Aristotle’s favored technical term for essence. It is an abbreviated way of saying ‘that which it was for an instance of kind K to be an instance of kind K,’ for instance ‘that which it was (all along) for a human being to be a human being’. In speaking this way, Aristotle supposes that if we wish to know what a human being is, we cannot identify transient or non-universal features of that kind; nor indeed can we identify even universal features which do not run explanatorily deep. Rather, as his preferred locution indicates, he is interested in what makes a human being human—and he assumes, first, that there is some feature F which all and only humans have in common and, second, that F explains the other features which we find across the range of humans. 