NATURE. - It is the intrinsic principle of the becoming of corporeal beings, especially according to Aristotle, who derives the term φύσις from φύσιναι, which means to be born, to sprout, to grow (Phys., II, 1, 193 b 16). Becoming (v.) belongs above all to living things, to the simple bodies that are called in the strict sense "natural bodies," to which are opposed things produced by art, by chance (ταὐτόματον) and by violence (βία): here phenomena occur without law and purpose because they are provoked from outside, whereas in nature becoming actualizes the subject in conformity with the law of its being. Therefore Aristotle defines nature as "the primary principle, intrinsic of itself, of motion and rest" (ibid., 192 b 20-22).
In the notion of nature Aristotle seeks to reconcile and overcome the opposition between the conception of the Presocratics, who admitted nothing but the materiality of beings, and the Platonic conception, which placed the laws of beings in the ideas and the principle of the movement of bodies in the soul. Therefore he declares that nature applies to matter, though not to indeterminate and empty matter, but to that "immediate matter which serves as subject for each of the beings that have in themselves the principle of motion and change" (ibid., 193 a 28). Nevertheless, in the proper sense nature is "the form and type (μορφὴ καὶ εἶδος) of the beings that have in themselves the principle of change," the form that is not separable (from matter) except conceptually (κατὰ λόγον; ibid., 193 b 2). In its immediate phenomenological sense nature was birth, as Empedocles (v.) said, opposed to death (fr. B, 8: Diels-Kranz, Die Fragmente der Vorsokr., 5th ed., I, Berlin 1937, p. 312); but Aristotle, who elsewhere cites the text of Empedocles (Met., V, 4, 1015 a ff.), fixed its metaphysical meaning within the sphere of becoming (against Plato) but beyond pure phenomena (against the conception of the Sophists). Hence nature is the essence (οὐσία) understood as the whole that exists and acts (ὅλη καὶ ἄπασα οὐσία: De Coelo I, 2, 268 b 11). St. Thomas completes this latter derived meaning, which in ordinary usage is the principal one, by appealing to Boethius, who gathered the Aristotelian physical-metaphysical process into a logico-metaphysical definition: "Natura est unamquamque rem informans specifica differentia" (De duabus naturis, cap. 1: PL 64, 1342; cf. Sum. Theol., 3ª, q. 2, a. 1). Taken in this rigor, the concept of nature enters Catholic theology in order to determine the relations in God among the three Divine Persons and the one identical divine nature, and in Jesus Christ between the Person of the Word, who subsists in two natures, the divine and the human assumed with the Incarnation: the clear distinction of the two natures entails the distinction of their respective operations and thus constitutes the foundation of merit and therefore of our redemption (ibid., q. 9, aa. 1-4).
St. Thomas also distinguishes a universal nature (which can be God or some other principle that moves the becoming of beings), which some call natura naturans, and a particular nature (cf. Averroes, In De coelo, I, 2, which has natura naturata): a terminology that would enjoy success with Spinoza (Ethica, part 1, prop. XXIX, scholion).