as Parmenides affirms. Thus we are in the midst of the fray; both parties are dragging us to their side; and we are not certain which of them are in the right; and if neither, then we shall be in a ridiculous position, having to set up our own opinion against ancient and famous men. Let us first approach the river-gods, or patrons of the flux. When they speak of motion, must they not include two kinds of motion, change of place and change of nature?--And all things must be supposed to have both kinds of motion; for if not, the same things would be at rest and in motion, which is contrary to their theory. And did we not say, that all sensations arise thus: they move about between the agent and patient together with a perception, and the patient ceases to be a perceiving power and becomes a percipient, and the agent a quale instead of a quality; but neither has any absolute existence? But now we make the further discovery, that neither white or whiteness, nor any sense or sensation, can be predicated of anything, for they are in a perpetual flux. And therefore we must modify the doctrine of Theaetetus and Protagoras, by asserting further that knowledge is and is not sensation; and of everything we must say equally, that this is and is not, or becomes or becomes not. And still the word 'this' is not quite correct, for language fails in the attempt to express their meaning. At the close of the discussion, Theodorus claims to be released from the argument, according to his agreement. But Theaetetus insists that they shall proceed to consider the doctrine of rest. This is declined by Socrates, who has too much reverence for the great Parmenides lightly to attack him. (We shall find that he returns to the doctrine of rest in the Sophist; but at present he does not wish to be diverted from his main purpose, which is, to deliver Theaetetus of his conception of knowledge.) He proceeds to interrogate him further. When he says that 'knowledge is in perception,' with what does he perceive? The first answer is, that he perceives sights with the eye, and sounds with the ear. This leads Socrates to make the reflection that nice distinctions of words are sometimes pedantic, but sometimes necessary; and he proposes in this case to substitute the word 'through' for 'with.' For the senses are not like the Trojan warriors in the horse, but have a common centre of perception, in which they all meet. This common principle is able to compare them with one another, and must therefore be distinct from them (compare Republic). And as there are facts of sense which are perceived through the organs of the body, there are also mathematical and other abstractions, such as sameness and difference, likeness and unlikeness, which the soul perceives by herself. Being is the most universal of these abstractions. The good and the beautiful are abstractions of another kind, which exist in relation and which above