CONTRADICTION (Principle, Law, or Axiom of), (contradico, to speak against; contradictio, ἀντίφασις).—
| It is usually expressed thus:—A thing cannot be and not be at the same time, or a thing must either he or not be, or the same attribute cannot at the same time he affirmed and denied of the same subject. Aristotle laid down this principle as the basis of all Logic, and of all Metaphysic (Metaph., lib. III. cap. III. sec. 3; lib. IX. cap. VII.; lib. X. cap. V.; lib. IV. cap. III. sec. 13; lib. IV. cap. V. sec. 59 ; lib. III. cap II. sec. 12; Analyt. Prin., II. 2, 53, B, 15). |
Attacked in ancient times by the Sceptics and Epicurus, and in the Middle Ages by the Scotists, it has been subjected by modern philosophers to a searching scrutiny. Locke repudiated it as useless for the purpose of attaining real knowledge, its only use being, according to him, didactic and argumentative (see Essay on Human Understanding, IV. 7), Leibnitz (Nouv. Essays, IV. 2, sec. 1) vindicated its value and its innate character against Locke’s attack. Considering it insufficient, however, as the basis of all truth and reasoning, he added the principle of the sufficient reason (q.v.). Kant thought this principle good only for those judgments of which the predicate is implied in the subject; or, as he called them, analytic judgments; as when we say, all body has extension. The idea of extension being implied in that of body, it is a sufficient warrant of the truth of such a judgment, that it implies no contradiction. In synthetic judgments, on the contrary, we rest either on à priori grounds of reason, or on the testimony of experience, according as they are à priori or a posteriori. Hegel considers it as the true expression of the procedure of thought at a certain stage—that of the ‘abstract’ understanding. But the distinctions which seem to understanding to be absolute are overcome by reason, which finds a deeper unity in the identity of opposites; and thus, though all thought proceeds according to the principle of contradiction, that principle is not to be taken as a final statement of truth, but only as its provisional expression (Logic of Hegel, Wallace, p. 189). Hamilton considers this principle, which he calls the law of non-contradiction, equally primary with that of Identity, the one being the positive and the other the negative expression of the same law (Lectures on Logic, I. 81-2).— V. IDENTITY. Ueherweg, System of Logic, pp. 235 ff, transl. by Lindsay.
