THREE:A principle in mechanics may be known, and even familiar to a learner, without being logically understood; it might even be said that both theory and practice may be learned without the power to connect and apply the two things. A person may, for example, understand the geometry of tooth gearing and how to lay out teeth of the proper form for various kinds of wheels, how to proportion and arrange the spokes, rims, hubs, and so on; he may also understand the practical application of wheels as a means of varying or transmitting motion, but between this knowledge and a complete wheel lies a long train of intricate processes, such as pattern-making, moulding, casting, boring, and fitting. Farther on comes other conditions connected with the operation of wheels, such as adaptation, wear, noise, accidental strains, with many other things equally as important, as epicycloidal curves or other geometrical problems relating to wheels.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 Theaettus 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 mans opinion is as good as anothers 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 rightwhich is a very different principle from holding that the majority should be obeyedwe 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.
