Plato, Phaedo

[101a] but you would insist that you say only that every greater thing is greater than another by nothing else than greatness, and that it is greater by reason of greatness, and that which is smaller is smaller by nothing else than smallness and is smaller by reason of smallness. For you would, I think, be afraid of meeting with the retort, if you said that a man was greater or smaller than another by a head, first that the greater is greater and the smaller is smaller by the same thing, and secondly, that [101b] the greater man is greater by a head, which is small, and that it is a monstrous thing that one is great by something that is small. Would you not be afraid of this?”

And Cebes laughed and said, “Yes, I should.”

“Then,” he continued, “you would be afraid to say that ten is more than eight by two and that this is the reason it is more. You would say it is more by number and by reason of number; and a two cubit measure is greater than a one-cubit measure not by half but by magnitude, would you not? For you would have the same fear.”

“Certainly,” said he.

“Well, then, if one is added to one [101c] or if one is divided, you would avoid saying that the addition or the division is the cause of two? You would exclaim loudly that you know no other way by which any thing can come into existence than by participating in the proper essence of each thing in which it participates, and therefore you accept no other cause of the existence of two than participation in duality, and things which are to be two must participate in duality, and whatever is to be one must participate in unity, and you would pay no attention to the divisions and additions and other such subtleties, leaving those for wiser men to explain. You would distrust [101d] your inexperience and would be afraid, as the saying goes, of your own shadow; so you would cling to that safe principle of ours and would reply as I have said. And if anyone attacked the principle, you would pay him no attention and you would not reply to him until you had examined the consequences to see whether they agreed with one another or not; and when you had to give an explanation of the principle, you would give it in the same way by assuming some other principle which seemed to you the best of the higher ones, and so on until [101e] you reached one which was adequate. You would not mix things up, as disputants do, in talking about the beginning and its consequences, if you wished to discover any of the realities; for perhaps not one of them thinks or cares in the least about these things. They are so clever that they succeed in being well pleased with themselves even when they mix everything up;