I have said that which was the first thing, that the knowledge of good is not virtue; and secondly, I have shown what virtue is, and in what it consists. It follows that I should show this also, that the philosophers were ignorant of what is good and evil; and this briefly, because it has been almost(1) made plain in the third book, when I was discussing the subject of the chief good. And because they did not know what the chief good was, they necessarily erred in the case of the other goods and evils which are not the chief; for no one can weigh these with a true judgment who does not possess the fountain itself from which they are derived.