ONE:After resolving virtue into knowledge of pleasure, the next questions which would present themselves to so keen a thinker were obviously, What is knowledge? and What is pleasure? The Theaet��tus is chiefly occupied with a discussion of the various answers already given to the first of these enquiries. It seems, therefore, to come naturally next after the Protagoras; and our conjecture receives a further confirmation when we find that here also a large place is given to the opinions of the Sophist after whom that dialogue is named; the chief difference being that the points selected for controversy are of a speculative rather than of a practical character. There is, however, a close connexion between the argument by which Protagoras had endeavoured to prove that all mankind are teachers of virtue, and his more general principle that man is the measure of all things. And perhaps it was the more obvious difficulties attending the latter view which led Plato, after some hesitation, to reject the former along206 with it. In an earlier chapter we gave some reasons for believing that Protagoras did not erect every individual into an arbiter of truth in the sweeping sense afterwards put upon his words. He was probably opposing a human to a theological or a naturalistic standard. Nevertheless, it does not follow that Plato was fighting with a shadow when he pressed the Protagorean dictum to its most literal interpretation. There are plenty of people still who would maintain it to that extent. Wherever and whenever the authority of ancient traditions is broken down, the doctrine that one man��s opinion is as good as another��s immediately takes its place; or rather the doctrine in question is a survival of traditionalism in an extremely pulverised form. And when we are told that the majority must be right��which is a very different principle from holding that the majority should be obeyed��we may take it as a sign that the loose particles are beginning to coalesce again. The substitution of an individual for a universal standard of truth is, according to Plato, a direct consequence of the theory which identifies knowledge with sense-perception. It is, at any rate, certain that the most vehement assertors of the former doctrine are also those who are fondest of appealing to what they and their friends have seen, heard, or felt; and the more educated among them place enormous confidence in statistics. They are also fond of repeating the adage that an ounce of fact is worth a ton of theory, without considering that theory alone can furnish the balance in which facts are weighed. Plato does not go very deep into the rationale of observation, nor in the infancy of exact science was it to be expected that he should. He fully recognised the presence of two factors, an objective and a subjective, in every sensation, but lost his hold on the true method in attempting to trace a like dualism through the whole of consciousness. Where we should distinguish between the mental energies and the physical processes underlying them, or between the207 elements respectively contributed to every cognition by immediate experience and reflection, he conceived the inner and outer worlds as two analogous series related to one another as an image to its original.Grinding, no doubt, if traced to the principles that lie at the bottom, is nothing more than a cutting process, in which the edges employed are harder than any material that can be made into cutters, the edges firmly supported by being imbedded into a mass as the particles of sand are in grindstones, or the particles of emery in emery wheels.

---