Physics

The intermediate seems more likely; for fire, earth, air, and water are already intertwined with contrarieties. Thus, those who make the subject different from these do not speak unreasonably, nor do those who make it air; for air has the least perceptible differences compared to others; next is water. But all of them shape this one thing with the opposites, such as density and rarity and by the more and the less. These are clearly, in general, excess and defect, as was said before. And this opinion seems to be ancient, that the one, the excess, and the defect are principles of existing things, although not in the same way; for the ancients said the two do the acting and the one does the receiving, while some of the later ones say the opposite, that the one does the acting and the two do the receiving. Therefore, to say there are three elements from these and similar observations would seem to have some reason, as we said, but more than three, no longer; for the one is sufficient for receiving. If, when there are four, there are to be two contrarieties, there will need to be some other intermediate nature for each of them. But if they can generate from each other being two, the other contrariety would be superfluous. At the same time, it is impossible for there to be more than the first contrarieties. For substance is one genus of being, so the principles would differ from each other only by priority and posteriority, but not in genus; for in one genus there is always one contrariety, and all contrarieties seem to be reducible to one. That the element is neither one nor more than two or three is clear; but which of these it is, as we said, presents much difficulty.

7. Let us speak in this way about all generation, having gone through it first; for it is according to nature to speak of common things first and thus consider the specific matters for each.