To ensnare the sophist of the Sophist in a definition disclosing him as a purveyor of images and falsehoods Plato must block the sophistical defence that image and falsehood are self-contradictory in concept, for they both embody the proposition proscribed by Parmenides — ‘What is not, is’. It has been assumed that Plato regards this defence as depending on a reading of ‘what is not’ (to mē on) in its very strongest sense, where it is equivalent to ‘what is not in any way’ (to mēdamōs on) or ‘nothing’. Likewise, the initial paradoxes of not-being (237b–239c) are seen as requiring that to mē on be understood in this way, that later designated by Plato (257b, 258e–259a) as the opposite of to on or ‘being’. On this interpretation, Plato's counter-strategy is to recognise a use of to mē on which is not opposed in this strict sense to being, but is indeed a part of it and is ‘being other than’.

In a stimulating article, R. W. Jordan challenges this account. I shall briefly attempt to show that his objections are not decisive and that his own interpretation is open to question.

Jordan makes the interesting suggestion (p. 120) that a distinction between two senses of not-being, where one is equivalent to nothing and one is not, dates from the middle dialogues — particularly from Republic V, where objects of agnoia are mēdamē onta and objects of doxa are both onta and mē onta. He concludes (p. 121), ‘Malcolm's view, then, seems to amount to this: that Plato is now extending the moral he draws about objects of belief (i.e. particulars) in the Republic to cover forms. Forms too now are seen to be both being and notbeing.’