CONTRADICTION, PRINCIPLE OF

The principle of contradiction expresses the metaphysical and logical opposition between being and its negation. It is concisely expressed by Aristotle: "A thing cannot at the same time be and not be…" (Meta. 996b30); "the same attribute cannot at the same time belong and not belong to the same subject in the same respect…" (Meta. 1005b 19–20). Formulated in the logical order, it asserts that it is impossible to affirm and at the same time deny the same predicate of the same subject.

Validity of the Principle. The principle of contradiction derives immediately from the abstract, intuitive apprehension of being. Since being conceptually involves a positive judgment or affirmation, it necessarily excludes its own negation. The principle of contradiction is consequently a priori, in a qualified sense, since its apprehension is implicit in the apprehension of being. Its necessity is notional and relational, expressing a basic incompatibility between the positive and the negative, between being and nonbeing. But being, as a transcendental value, extends to every aspect of reality, and intuition of it is implicit in every cognitive act involving thought. Therefore, the principle of contradiction, even though it be regarded as a formal law, has at the same time a concrete universal reference. It is valid for every order of being as well as of knowledge; for every process in the realm of the concrete, the particular, and the practical; in the metaphysical, physical, and moral spheres; in the fields of mathematics, science, and history. Its universal, formal validity is confirmed by concrete experimental evidence, such as that showing the mutual exclusiveness of sweet and sour, healthy and unhealthy, democracy and dictatorship.

The principle of contradiction displays its rigor and its richness above all in metaphysics. This principle alone can initiate the analytic-synthetic process involved in elaborating the concept of being. Under its influence being is grasped in its intrinsic intelligibility, in its absolute condition, and in its possibilities for extension and participation; in the profound interior connection of its constituent principles, essence and existence; in the relationships that are established between being as a substance and its qualitative and operative determinations, whether these be necessary or contingent; and, finally, in its ultimate explanation and absolute foundation—the unparticipated, absolute Being.

Primacy of the Principle. Because of its immediate derivation from the concept of being and its great importance in metaphysics, epistemology, and logic, St. thomas aquinas gives the principle of contradiction priority over all other axioms and principles: "For that which first falls under apprehension is being, the understanding of which is included in all things whatsoever a man apprehends. Therefore, the first undemonstrable principle is that the same thing cannot be affirmed and denied at the same time, which is based on the notions of being and not-being; and on this principle all others depend" (Summa Theologiae 1a2ae, 94.2; cf. Aristotle, Meta. 1005b 32–34). It is the norm and basis of every affirmation, truth, and certainty. It cannot be demonstrated because it is based on a primary concept, i.e., one incapable of logical derivation. It cannot even be denied, because whoever tries to deny it assumes that to affirm is not the same as to deny, and thus implicitly presupposes the principle. Consequently, it is possible to clarify its character only as absolutely intrinsic to understanding itself, and to give an indirect defense of the principle by demonstrating its inevitable acknowledgment by one who attempts to refute it. If the principle of contradiction is rejected, nothing can be affirmed or denied; no expression will any longer have a determined meaning. And, to quote Aristotle, "If words have no meaning our reasoning with one another, and indeed with ourselves, has been annihilated; for it is impossible to think of anything if we do not think of one thing" (Meta. 1006b 8–10). The rejection of this principle thus involves the negation of being in the metaphysical order and the denial of thought content in the logical order.

The principle of contradiction is commonly assumed to have priority and precedence over the principle of identity. From a logical point of view the principle of identity, even when expressed in a nontautological formula such as "being is determined in itself," is dialectically inert. It is not even psychologically first, for in the order of knowledge the original concept of being is followed immediately by the concept of its negation or opposition; hence the principle of contradiction is first known, and this is a relational synthesis of the positive with the negative.

The principle of contradiction comes first as a universal rule of thought, as well as of the dialectical process with which thought penetrates being and conforms itself to it (see dialectics). This primacy is not to be confused with that of the first ontological principle, the absolute, which is the all-comprehensive principle of truth; nor does it imply a rigorous and strictly psychological innatism. The principle of contradiction, in itself, is not the positive source of advances in theoretical knowledge, nor is it productive of thought content or of solutions to particular problems. Instead, it is the condition of the existence and intelligibility of all knowledge, truth, doubt, or certitude in the human intellect. Again, the principle is not something concrete in reality; it exists rather in the logical-objective order and in intellectual conscious ness of the nature of being.

Erroneous Interpretations. The limitations found in the principle of contradiction by some thinkers seem traceable either to inexact expressions of the principle or to exclusively metaphysical interpretations of it. In the philosophy of Aristotle and in traditional, substantialistic, and pluralistic philosophies, the principle of contradiction does receive a plainly ontological interpretation. Thus it is sometimes formulated as the "principle of the determination of substance," according to which every being is definitely constituted in itself as an ontologicaloperative principle, specifically and numerically distinct from every other being. For this reason Aristotle remarks that those who deny the principle of contradiction "do away with substance and essence" (Meta. 1007a 20–21). Yet monistic conceptions of reality, like that of spinoza, while not rejecting this principle, necessarily give it a different value and interpretation. In pantheism and ideal ism as well, it retains its validity relative to the phenomenal manifestations of being; but when nature and the foundation of reality are concerned, diversities and contradictions become dissolved in an original and absolute unity. Accordingly, the meaning of the principle of contradiction changes in the Hegelian dialectical interpretation of reality. For hegel, a concrete being is the moment of unity that being and nothingness assume in becoming. In its concrete becoming, reality is a necessary and perpetual synthesis of opposites and contradictories. Hegel thus introduces contradiction into the intimate structure of the real as its most profound and essential determination. Opposites are present not in an objective identity, but rather as overcome in the evolving and creative unity of being. What is real neither is, nor subsists, in contradiction, but necessarily passes through it.

The basic meaning of the principle of contradiction, as already explained, is not refuted by any philosophical system. It is not inconsistent with Hegelianism, nor with logical positivism, which holds that laws and metaphysical statements express only verbal relations and not the structure of the real. Hegel's critique, however, betrays at least the possibility of an incorrect interpretation of the principle of contradiction. This must not be understood as a principle of the unchangeability and stability of being, or as a negation of the process of becoming. Motion and multiplicity, diversity and composition, are essential to finite being and are quite evident in the universe. Hence, in the ontological unity of every finite being, a coexistence and succession in time of indefinite, qualitative determinations, both operative and relational, are possible and real, though sometimes in themselves opposed. It is in this sense that even man is called "a living contradiction." One must keep sight of the reality of cosmic and human experience to understand the real meaning of contradiction in being, whether spiritual or material. Such experience does not question, and consequently does not weaken, the universal validity of the principle of contradiction.

See Also: first principles.

Bibliography: u. viglino, Enciclopedia filosofica, 4 v. (Venice-Rome 1957) 1:1223–26. j. laminne, "Le Principe de contradiction et le principe de causalité," Revue Néo-scolastique de philosophie 19 (1912) 435–88. l. fuetscher, "Die ersten Seinsund Denkprinzipien," Philosophie und Grenzwissenschaft 3 (1930) 93–376. j. marÉchal, Le Thomisme devant la philosophie critique (2d ed.) 491–504, 561–68, v.5 of Le Point de départ de la métaphysique, 5 v. (3d ed. Paris 1944–49). m. versfeld, The Mirror of Philosophers (New York 1960). f. h. bradley, The Principles of Logic, 2 v. (2d ed. London 1922).

[u. viglino]