but in enacting laws the real object is to make them as advantageous to itself as possible, but what is advantageous regards also the future, for laws are enacted that they may be advantageous for the future. But if man is the measure of all things, he must also contain within himself the criterion of things about to happen; yet it will be admitted, in a variety of instances that are adduced, that a person who is skilled is better able to judge of the future than one who is unskilled: and Protagoras himself can judge beforehand better than any private person what arguments are likely to be available in a court of justice, so that not every man, but the wise man only, is the true measure of things[1].
This part of the argument being brought to a close, Socrates next proposes to consider the essence that is said to consist in motion, a doctrine which the followers of Heraclitus were then advocating very strenuously. Now there are two species of motion, removal and change; the former is when a thing passes from one place to another, the latter a change of quality, as when a thing becomes black from white, or hard from soft; and all things must undergo both kinds of motion, otherwise the same thing would be both in motion and at rest at the same time, and in that case it would not be more correct to say that all things are in motion than that they are at rest. Since then every thing must be continually undergoing a process of change at the same time that it is in motion, there can be nothing fixed and certain, so that perception cannot be science, for, as all things are in motion, perception itself, which results from the relation between the object and the percipient, must be in a constant state of motion and change[2].
Theætetus now resumes the argument, and though it would seem that Protagoras's doctrine had been already sufficiently refuted, yet Socrates resolves to try it by one more test. Each sense has its peculiar perception, and such things as are perceived by one faculty cannot be perceived by another; for instance, what is perceived by hearing cannot be perceived by
