Aristotle, Metaphysics

[1004b] [1] If this is not so, who is it who in will investigate whether " Socrates" and " Socrates seated" are the same thing; or whether one thing has one contrary, or what the contrary is, or how many meanings it has?¹ and similarly with all other such questions.Thus since these are the essential modifications of Unity qua Unity and of Being qua Being, and not qua numbers or lines or fire, clearly it a pertains to that science² to discover both the essence and the attributes of these concepts.And those who investigate them err, not in being unphilosophical, but because the substance, of which they have no real knowledge, is prior. For just as number qua number has its peculiar modifications, e.g. oddness and evenness, commensurability and equality, excess and defect, and these things are inherent in numbers both considered independently and in relation to other numbers; and as similarly other peculiar modifications are inherent in the solid and the immovable and the moving and the weightless and that which has weight; so Being qua Being has certain peculiar modifications, and it is about these that it is the philosopher's function to discover the truth. And here is evidence of this fact.Dialecticians and sophists wear the same appearance as the philosopher, for sophistry is Wisdom in appearance only, and dialecticians discuss all subjects, [20] and Being is a subject common to them all; but clearly they discuss these concepts because they appertain to philosophy.For sophistry and dialectic are concerned with the same class of subjects as philosophy, but philosophy differs from the former in the nature of its capability and from the latter in its outlook on life. Dialectic treats as an exercise what philosophy tries to understand, and sophistry seems to be philosophy; but is not.

Further, the second column of contraries is privative, and everything is reducible to Being and Not being, and Unity and Plurality; e.g. Rest falls under Unity and Motion under Plurality. And nearly everyone agrees that substance and existing things are composed of contraries; at any rate all speak of the first principles as contraries—some as Odd and Even,³ some as Hot and Cold,⁴ some as Limit and Unlimited,⁵ some as Love and Strife.⁶ And it is apparent that all other things also are reducible to Unity and Plurality (we may assume this reduction);