BODY. — In general, a body is a material, sensible reality. In experimental science, a body is a portion of matter with specific properties (dimensions, weight, density, chemical reactions, etc.). Simple bodies and compound bodies are distinguished (v. *Compound*).
Philosophically, the body is a material substance, that is, a reality that subsists in itself and is perceptible through the senses.
The speculation on the essence and constitutive principles of bodies constitutes, as is well known, the main object of early Greek philosophy. The ancient Ionians posited as the foundation of material reality a common principle (*ἀρχή*, *φύσις*) from which bodies 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 (*ἀπείρων*); for Anaximenes, air (ibid., *Met.*, I, 3, 983 b). The Pythagoreans, instead, maintained that the principle of which bodies are made is number (ibid., I, 5, 983 b). According to Empedocles, compound bodies result from the mechanical composition of elements (earth, water, air, fire), divided into particles and immutable (*Fgm.* 8, 9, 11); similarly, Anaxagoras, who admitted infinite, indefinitely divisible elements (*Fgm.* 1, 4, 17). The atomists (Leucippus and Democritus) held that the primordial bodies are atoms, essentially simple, indivisible, immutable, and of different shapes; these, combining in various ways, give rise to all bodies (cf. Aristotle, *Met.*, I, 4, 985 b 5 ff.; V. *ATOMISM*).
For Plato, bodies, which are various and mutable, are participation or imitation of immutable, subsistent ideas; bodies consist of space (*χώρα*), which remains immutable amid the change of bodies, as a kind of "receptacle" (*ὑποδοχή*), a "nurse" (*τύχημη*), an "imprint-bearer," receiving all forms (*μορφή*) without having any of its own (*ἀμορφον*): *Tim.*, 48 e and 52 d). These notions, obscure in Plato, are developed by Aristotle, for whom the body is essentially a compound (*σύνολο*) of a substratum, called matter (*ὕλη*), and a form (*μορφή*): *γίγνεται πᾶν ἐκ τοῦ ὑποκειμένου κατὰ τὴν μορφήν* (*Phys.*, I, 7, 190 b 20).
Matter is the substratum of the changes of bodies (ibid., I, 9, 192 a 31). It is in itself indeterminate: "I call matter that which in itself is not a determinate thing, nor quantity, nor any other determination of being" (*Met.*, VII, 3, 1029 a 20). Form is the determinate and determining element: it is not a complete being, 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 to the Greek, Arabic, and Latin Aristotelian schools and was developed by St. Thomas Aquinas, who clarified its consequences. It was substantially modified by Scotus, who denied that prime matter is pure potentiality with respect to every act (Opus Oxoniense, II, d. 12, q. 1, 2, in *Opera omnia*, ed. L. Wadding, VI, Lyon 1639, p. 664 ff.), and similarly by F. Suárez (*Disputationes metaphysicae*, d. 13, s. 5: in *Opera omnia*, ed. L. Vivès, XXV, Paris 1856-61, p. 414 ff.) and their schools.
In modern philosophy, Descartes' position is well known, according to which the body is essentially extension: "We perceive the nature of matter or of body in general not to consist in that it is a hard thing... but only in that it is a thing extended in length, breadth, and depth" (*Principia philosophiae*, II, n. 4: in *Opera omnia*, ed. C. Adam and P. Tannery, VIII, Paris 1897-1910, p. 42); thus it has only the dimensional properties of matter, divisibility, motion, figure, etc. For Spinoza, the body is a mode of the single, infinite substance, considered insofar as it is extended: "By body I understand a mode which expresses God’s essence, in so far as it is considered as extended, in a certain and determinate way" (*Ethics*, ed. G. Gentile, Bari 1933, p. 47). Leibniz conceives the body as an aggregate of monads, simple, active substances; consequently, its extension is phenomenal (cf. Letter to M. Arnaud, ed. Dutens, II, part 1, Geneva 1768, p. 46).
In the English school, Berkeley’s position is notable for its resolute immaterialism, according to which the body is a complex of impressions caused in our spirit by God: "The ideas imprinted on our spirits by the Author of nature are called real things" (*A Treatise Concerning the Principles of Human Knowledge*, § 33: Italian trans. by G. Papini, Bari 1925, p. 40). "Their esse (of sensible things) is percipi, and it is not possible that they should have any existence outside the minds or thinking things which perceive them" (ibid., § 3, ed. cit., p. 26). For D. Hume, the opinion of the continued existence, and thus distinct from us, of bodies arises not from the senses but from the coherence and constancy of certain impressions which, returning always the same, we suppose "are connected in a real existence, of which, however, we are not conscious" (*A Treatise of Human Nature*, I, part 4, sect. 2, § 6: Italian trans. by A. Carlini, Bari 1926, p. 245). In conclusion, Hume’s skepticism "is forced to admit the existence of bodies, though it cannot claim to support, with any philosophical argument, their reality" (ibid., § 1: ed. cit., p. 231).
According to I. Kant, the body or nature is the thing as perceived by us through the a priori forms, not the thing in itself: "By ‘nature’ is understood the existence of things insofar as it is determined by universal laws. If ‘nature’ meant the existence of things in themselves, we could never know it, either a priori or a posteriori" (*Prolegomena to Any Future Metaphysics*, Italian trans. by P. Martinetti, Bari 1924, p. 92). In Hegel, bodies (nature) are the first externalization of the Idea from itself, its becoming other than itself, spreading out in space and time; only after this externalization does the Idea return to itself, knowing itself, and becomes thought of itself, that is, Spirit (*Encyclopedia of the Philosophical Sciences in Outline*, Italian trans. by B. Croce, Bari 1923, p. 199). G. Gentile thinks that bodies are the spatial and temporal world, the world of the many, nature, which is outside the Spirit but is its life: "Nature... is intelligible only as the life of the Spirit, which indeed multiplies itself but remains one" (*Teoria generale dello Spirito*, Florence 1938, p. 126). On the other hand, for materialism the body is the only existing reality, from which everything derives; and for phenomenism, it is a mere complex of sensitive and subjective representations.
In modern physics, bodies are conceived as aggregates of extended particles, which are the fundamental constitutive elements of matter, bound together by forces; the recent theory of quantum mechanics, while accepting the particulate constitution of matter, conceives the body as a complex of particle-waves, which in compound bodies lose their physical individuality (v. *matter*). These scientific theories leave open the philosophical problem of the ontological unity of the compound body.
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