CORPO. – In general, c. is a material, perceptible reality. In experimental science, c. is a portion of matter with certain specific properties (dimensions, weight, density, chemical reactions, etc.). Simple and compound c. are distinguished (v. composto). Philosophically, c. is a material substance, that is, a reality subsisting in itself, perceptible through the senses.
Speculation concerning the essence and constitutive principles of c. constitutes, as is well known, the principal subject of early Greek philosophy. The ancient Ionians placed at the foundation of material reality a common principle (ἀρχή, φύσις), from which c. originate and to which they return, variously modified (cf. Aristotle, Phys., I, 4, 187 a 12 ff.). For Thales this principle is water; for Anaximander, the infinite (ἄπειρον); for Anaximenes, air (id., Met., I, 3, 983 b). The Pythagoreans, on the other hand, maintained that the principle of which c. are made is number (ibid., I, 5, 983 b). According to Empedocles, compound c. result from the mechanical composition of the elements (earth, water, air, fire), divided into particles and immutable (Prgm. 8, 9, 11); similarly Anaxagoras, who admitted infinitely many elements, indefinitely divisible (Prgm. 1, 4, 17). The atomists (Leucippus and Democritus) held that the primordial c. are atoms, essentially simple, indivisible, immutable, and differing in form; by combining in various ways, these give rise to all c. (cf. Aristotle, Met., I, 4, 985 b 5 ff.; V. ATOMISMO). For Plato, c., various and mutable, are participations in or imitations of the subsistent and immutable ideas; c. consist of space (χώρα), which remains unchanged amid the changing of c., and is like a “receptacle” (ὕποδοχῆ), a “nurse” (τιθήμῳ), a “bearer of impressions”; it receives all forms (μορφῆ) into itself without having a form of its own (ἄμορφον δν: Tim., 48 e and 52 d). These notions, obscure in Plato, are developed by Aristotle, for whom c. is essentially composed (σύνελον) of a substratum, called matter (ὕλη), and of a form (μορφῆ): γίγνεται πᾶν ἐκ τε τοῦ ὑποκειμένου καὶ τῆς μορφῆς (Phys., I, 7, 190 b 20).
Matter is the substratum of the changes undergone by c. (ibid., I, 9, 192 a 31). In itself it is indeterminate: “I call matter that which in itself is neither a determinate thing, nor quantity, nor any other of the determinations of being” (Met., VII, 3, 1029 a 20). Form is the determined and determining element: it is not a complete entity, nor is it generated in the proper sense (ibid., VIII, 3, 1043 b 15; 5, 1044 b 21-23, etc.). This doctrine of hylomorphism (v.) passed into the Greek, Arab, and Latin Aristotelian schools and was developed by S. Tommaso, who clarified its consequences. It was instead substantially modified by Scotus, who denied that prime matter is pure potency with respect to every act (Opus Ocon., II, d. 12, q. 1, 2, in Opera omnia, ed. L. Wadding, VI, Lyon 1639, p. 664 ff.), and similarly by F. Suárez (Disputaciones metaphysicae, d. 13, s. 5: in Opera omnia, ed. L. Vivés, XXV, Paris 1856-61, p. 414 ff.) and by their schools.
In modern philosophy, the position of Descartes is well known, according to which c. is essentially extension: “Percipie-mus naturam materiae sive corporis in universum spectati non consistere in eo quod sit res dura... sed tantum in eo quod sit res extensa in longum, latum et profundum” (Principia philosophiae, II, n. 4: in Opera omnia, ed. C. Adam and P. Tannery, VIII, Paris 1897-1910, p. 42); hence it has only the dimensional properties of matter, divisibility, motion, figure, etc. For Spinoza, on the other hand, c. is a mode of the one, infinite Substance, considered insofar as it is extended: “Per corpus intelligo modum, qui Dei essentiam, quatenus ut res extensa consideratur, certo et determinato modo exprimit” (Ethica, ed. G. Gentile, Bari 1933, p. 47). Leibniz conceives c. as an aggregate of monads, simple and active substances; consequently, its extension is phenomenal (cf. Lettera a M. Arnauld, ed. Dutens, II, part 1, Geneva 1768, p. 46).
In the English school, Berkeley’s position deserves note for its pronounced immaterialism: for him, c. is a complex of impressions caused in our spirit by God: “The ideas impressed upon our spirit by the author of nature are called real things” (Trattato dei principi della conoscenza umana, n. 33: Italian trans. by G. Papini, Bari 1925, p. 40). “Their esse (of sensible things) is percipi, and it is impossible that they should have existence outside the minds or thinking things that perceive them” (ibid., n. 3, ed. cit., p. 26). For D. Hume, the belief in the continued existence, and hence in the existence distinct from us, of c. arises not from the senses but from the coherence and constancy of certain impressions which, returning always identical, we suppose “to be connected in a real existence, of which, nevertheless, we are not conscious” (Trattato sulla natura umana, I, part 4, section 2, n. 6: trans. by A. Carlini, Bari 1926, p. 245). In conclusion, Hume’s skepticism “is forced to admit the existence of c., although it cannot claim to uphold their reality by any philosophical argument” (ibid., n. 1: ed. cit., p. 231).
According to E. Kant, c., or nature, is the thing insofar as it is perceived by us through the a priori forms, not the thing in itself: “By nature is understood the existence of things insofar as determined by general laws. If ‘nature’ signified the existence of things in themselves, we could never know it, either a priori or a posteriori” (Prolegomeni a ogni metafisica futura, trans. by P. Martinetti, Bari 1924, p. 92). In Hegel, c. (nature) are the first externalization of the Idea from itself, its becoming other than itself by extending itself in space and time; only after this externalization does the Idea return into itself, knowing itself, and become thought of itself, that is, Spirit (Enciclopedia delle scienze filosofiche in compendio, trans. by B. Croce, Bari 1923, p. 199). G. Gentile thinks that c. are the spatial and temporal world, the world of multiplicity, nature, which is outside Spirit but is its life: “Nature... is intelligible only as the life of Spirit, which multiplies itself, indeed, but while remaining one” (Teoria generale dello Spirito, Florence 1938, p. 126). For materialism, on the other hand, c. is the only existing reality, from which everything derives; and for phenomenalism, it is a pure complex of sensitive and subjective representations.
In modern physics, c. are conceived as aggregates of extended particles, which are the fundamental constituent elements of matter, bound together by forces; recent quantum-mechanical theory, while accepting the particulate constitution of matter, regards c. as a complex of wave-particles which, in compound c., lose their physical individuality (v. MATERA). These scientific theories leave open the philosophical problem of the ontological unity of compound c.