PYTHAGORAS TO PLATO surely have to be superior to it in the way that the Idea of F is superior to all the non-ideal Fs The notion of stratiWed relationships between Ideas opens up a Pandora’s box which Plato, when presenting the classical Theory of Ideas in his central dialogues, preferred to keep closed The Principle of Uniqueness is sometimes stated in a misleading way by commentators Plato frequently says that only Ideas really are, and that the non-ideal particulars we encounter in sense-experience are between being and not being He is often taken to be saying that only Ideas really exist, and that tangible objects are unreal and illusory In context, it is clear that when Plato says that only Ideas really are, he does not mean that only Ideas really exist, but that only the Idea of F is really F, whatever F may be in the particular case Particulars are between being and not being in that they are between being F and not being F—i.e they are sometimes F and sometimes not F.27 For instance, only the Idea of Beauty is really beautiful, because particular beautiful things are (a) beautiful in one respect but ugly in another (in Wgure, say, but not in complexion), or (b) beautiful at one time but not another (e.g at age 20 but not at age 70), (c) beautiful by comparison with some things, but not with others (e.g Helen may be beautiful by comparison with Medea, but not by comparison with Aphrodite), (d) beautiful in some surroundings but not in others (Smp 211 a–e) An important feature of the classical Theory of Ideas is the Principle of Sublimity The particulars that participate belong to the inferior world of Becoming, the world of change and decay; the Ideas that are participated in belong to a superior world of Being, of eternal stability The most sublime of all Ideas is the Idea of the Good, superior in rank and power to all else, from which everything that can be known derives its being (Rep 509c) The problem with the Theory of Ideas is that the principles that deWne it not seem to be all consistent with each other It is diYcult to reconcile the Principle of Separation with the Principles of Commonality and of SelfPredication The diYculty was Wrst expounded by Plato himself in the Parmenides, where he gives an argument along the following lines Let us suppose that we have a number of particulars, each of which is F Then, by (1) there is an Idea of F This, by (3), is itself F But now the Idea of F and the original particular Fs make up a new collection of F things By (1) again, this 27 I Wrst learnt this from Vlastos’s article ‘Degrees of Reality in Plato’, in R Bambrough (ed.), New Essays on Plato and Aristotle (London: Routledge & Kegan Paul, 1965) 53