no discourse if there were no communion. For the Sophist, although he can no longer deny the existence of not-being, may still affirm that not-being cannot enter into discourse, and as he was arguing before that there could be no such thing as falsehood, because there was no such thing as not-being, he may continue to argue that there is no such thing as the art of image-making and phantastic, because not-being has no place in language. Hence arises the necessity of examining speech, opinion, and imagination. And first concerning speech; let us ask the same question about words which we have already answered about the kinds of being and the letters of the alphabet: To what extent do they admit of combination? Some words have a meaning when combined, and others have no meaning. One class of words describes action, another class agents: 'walks,' 'runs,' 'sleeps' are examples of the first; 'stag,' 'horse,' 'lion' of the second. But no combination of words can be formed without a verb and a noun, e.g. 'A man learns'; the simplest sentence is composed of two words, and one of these must be a subject. For example, in the sentence, 'Theaetetus sits,' which is not very long, 'Theaetetus' is the subject, and in the sentence 'Theaetetus flies,' 'Theaetetus' is again the subject. But the two sentences differ in quality, for the first says of you that which is true, and the second says of you that which is not true, or, in other words, attributes to you things which are not as though they were. Here is false discourse in the shortest form. And thus not only speech, but thought and opinion and imagination are proved to be both true and false. For thought is only the process of silent speech, and opinion is only the silent assent or denial which follows this, and imagination is only the expression of this in some form of sense. All of them are akin to speech, and therefore, like speech, admit of true and false. And we have discovered false opinion, which is an encouraging sign of our probable success in the rest of the enquiry.