Let us now come to the question of the knowledge of good and evil. But we must say a few words by way of preface. It appears to me that they who speak so positively about those questions of natural philosophy, do not reflect that they are depriving themselves of the authority of those ideas which appear more clear. For they cannot give a clearer assent to, or a more positive approval of the fact that it is now daylight, than they do, when the crow croaks, to the idea that it is commanding or prohibiting something. Nor will they affirm that that statue is six feet high more positively after they have measured it, than that the sun, which they cannot measure, is more than eighteen times as large as the earth. From which this conclusion arises: if it cannot be perceived how large the sun is, he who assents to other things in the same manner as he does to the magnitude of the sun, does not perceive them. But the magnitude of the sun cannot be perceived. He, then, who assents to a statement about it, as if he perceived it, perceives nothing. Suppose they were to reply that it is possible to perceive how large the sun is; I will not object as long as they admit that other things too can be perceived and comprehended in the same manner. For they cannot affirm that one thing can be comprehended more or less than another, since there is only one definition of the comprehension of everything. XLII. However, to go back to what I had begun to say—What have we in good and bad certainly ascertained? (we must, of course, fix boundaries to which the sum of good and evil is to be referred;) what subject, in fact, is there about which there is a greater disagreement between the most learned men? I say nothing about those points which seem now to be abandoned; or about Herillus, who places the chief good in knowledge and science: and though he had been a pupil of Zeno, you see how far he disagrees with him, and how very little he differs from Plato. The school of the Megaric philosophers was a very celebrated one; and its chief, as I see it stated in books, was Xenophanes, whom I mentioned just now. After him came Parmenides and Zeno; and from them the Eleatic philosophers get their name. Afterwards came Euclid of Megara, a pupil of Socrates, from whom that school got the name of Megaric. And they defined that as the only good which was always one, alike, and identical. They also borrowed a great deal from Plato. But the Eretrian philosophers, who were so called from Menedumus, because he was a native of Eretria, placed all good in the mind, and in that acuteness of the mind by which the truth is discerned. The Megarians say very nearly the same, only that they, I think, develop their theory with more elegance and richness of illustration. If we now despise these men, and think them worthless, at all events we ought to show more respect for Ariston, who, having been a pupil of Zeno, adopted in reality the principles which he had asserted in words; namely, that