"You must not, then," he continued, "consider this only with respect to men, if you wish to ascertain it with greater certainty, but also with respect to all animals and plants, and, in a word, with respect to every thing that is subject to generation. Let us see whether they are not all so produced, no otherwise than contraries from contraries, wherever they have any such quality; as, for instance, the honorable is contrary to the base, and the just to the unjust, and so with ten thousand other things. [42]. Let us consider this, then, whether it is necessary that all things which have a contrary should be produced from nothing else than their contrary. As, for instance, when any thing becomes greater, is it not necessary that, from being previously smaller, it afterward became greater?"
"And if it becomes smaller, will it not, from being previously greater, afterward become smaller?"
"It is so," he replied.
"And from stronger, weaker? and from slower, swifter?"
"Certainly."
"What, then? If any thing becomes worse, must it not become so from better? and if more just, from more unjust?"
"How should it not?"
"We have then," he said, "sufficiently determined this, that all things are thus produced, contraries from contraries?"
"Certainly."