METAPHYSICS objections an Aristotelian would make against a Platonist It seems diYcult to render Aquinas’ teaching coherent on this topic, other than by saying that he is an Aristotelian on earth, but a Platonist in heaven The most important way in which Aquinas, for better or worse, ampliWes the Aristotelian system of potentiality and actuality is by applying it to the pair of concepts essence and existence, which he took over from Avicenna For Aquinas, as for Avicenna, there are not just generic essences, such as humanity, but also the individual humanities of Peter and Paul There are also two diVerent kinds of existence, or two diVerent senses of ‘esse’, the Latin verb ‘to be’ when it is used as equivalent to ‘exist’ There is, Wrst, generic existence, the existence of a kind of thing: as in ‘Angels exist’ or ‘There are angels’ There is also the individual existence of particular objects as in ‘The Great Pyramid still exists, but the Pharos of Alexandria does not’ (In Latin the use of ‘est’ and ‘non est’ is quite natural in such contexts; but in English ‘Rome is, but Troy is not’ has an archaic Xavour.) Generic existence is the kind of existence that philosophers, since Kant, have insisted ‘is not a predicate’; it is expressed in modern logic by the use of the particular quantiWer (for some x, x is an angel) Individual existence, on the other hand, is a perfectly genuine predicate.5 With regard to generic existence, Aquinas’ teaching is quite clear A classic text is from De Ente et Essentia: Whatever [belongs to a thing and] is not part of the concept of an essence or quiddity is something that arrives from outside and is added to the essence; because no essence can be conceived without the elements which are parts of the essence But every essence or quiddity can be conceived without anything being understood with respect to its existence; for I can understand what a human being is, or what a phoenix is, and yet be ignorant whether they have existence in the nature of things Hence it is clear that existence is diVerent from essence or quiddity (DEE 94–105) Whether there are things of a certain kind is quite a diVerent issue from what things of that kind are: whether there are any angels is not at all the same question as what ‘angel’ means If this is what is meant by saying that essence and existence are really distinct, then the doctrine is undoubtedly correct In my book Aquinas on Being (Oxford: Oxford University Press, 2002) I have listed twelve diVerent senses of ‘esse’ in Aquinas 199