necessarily accompanied by contradiction in the linguistic sense, because one contrary negates the other: its presence entails the absence of the other, just as the presence of blackness entails the absence of whiteness.

In the terminology of many theoretical thinkers, two contradictories are things that cannot coexist and cannot both be absent. Two contraries cannot coexist, but may both be absent.

In the terminology of others, however, contradictories are negation and affirmation alone, as when you say, “Either it is, or it is not.” Hence their definition: “Contradiction is a difference between two propositions in negation and affirmation, such that the truth of either entails the falsity of the other.”

Thus, contradiction in the usage of the former group is broader than in that of the latter. Two things that cannot coexist and cannot both be absent may both be positive, both be privative, or consist of something’s presence and its absence. Even if one is existence and the other nonexistence, they may be expressed in affirmative terms that do not, in themselves, indicate contradiction in the narrower sense. For example, one may say of something existent: “It is either self-subsisting or subsists in another; it is either intrinsically necessary or intrinsically contingent; it is either eternal or originated,” and so forth.

It is well known that dividing what exists into the self-subsisting and that which subsists in another, the necessary and the contingent, or the eternal and the originated is an exhaustive division, just as dividing what is known into what is affirmed and what is negated is exhaustive. The two alternatives in each division cannot coexist and cannot both be absent, just as existence and nonexistence cannot coexist and cannot both be absent.