INTELLECT. — It is the principle of the thought of human consciousness that distinguishes man from the lower forms of life.
The first affirmation of the intellect as a supersensible activity is due to Anaxagoras (Aristotle, Met., I, 3, 984 b 15), who nevertheless limits himself to conceiving the intellect (νοῦς) as the “cause of the order of the cosmos” and the principle of the movement and separation of things (H. Diels-W. Kranz, Die Fragmente der Vorsokratiker, II, 5th ed., Berlin 1935, B 13, p. 39). It is a controversial question whether Democritus admitted a distinction in nature between intellect and sense; it nevertheless seems that the fundamental principle of his theory of knowledge—“like is known by like” (ὕμοιον ὁμοίω)—is nothing other than the application of the principle common to the interaction of beings (cf. Aristotle, De gen. et care., I, 7, 323 b 10 ff.). Having been deepened in its constitutive function of truth by Platonic idealism, the intellect is referred by Aristotle intrinsically to sensible experience in its representative syntheses (φαντάσματα; cf. De an., III, 3, 428 a 1; ibid., 7, 431 a 17): but Aristotle left unresolved the problem of the personal individuality of the intellect. Neoplatonism, in its attempt at a synthesis between Plato and Aristotle, conceived the intellect as the second hypostasis between the One-Good and the Soul: Plotinus calls the intellect the “first act of the Good,” which circulates around the Good, while the Soul looks toward the intellect and through it reaches God (Enn., 1, 8; ed. E. Bréhier, I, Paris 1924, p. 116, 21 ff.). Plotinus and the entire Neoplatonic school labored to reconcile the separation established by Plato between Ἰωσσοφηλός and Ἰαραδείγματα, and a single theory has still not been found. In Proclus, who gathers the results of the tradition in a more systematic form, there are three degrees or moments of the intellect: a) first there is a δεῖον νοητὸν, which is the principle of the intelligible and transcends it: ἢ νοητὸν κατ' αἰτίαν; b) this is followed by the νοῦς νοητὸς, in which subject and object are ἐν κατ' ἀριθμῶν, and which is the first and principal intellect (πρῶτος, ἀμφέβητος νοῦς); c) finally there are the participating intellects, or κατὰ μέθῃςν, in which subject and object are distinct (cf. Procl., The elements of theology, ed. E. R. Dodds, Oxford 1933, p. 285 ff.).
The problem of the intellect forms, so to speak, the central theme of the historical development of Aristotelianism: the discussions concern above all the interpretation of chapter 5 of Book III of De anima, in which Aristotle distinguishes two intellects in the soul, just as in every nature two principles are distinguished:
one passive, matter, which is in potency to everything; the other, which is like “cause and agent” (τὸ αἴτιον καὶ ποιητικῶν). Thus there is one intellect to which it belongs to become all things (ὁ νόῳ... τῷ πάντα γίνεσθαι), and another to which it belongs to make all things intelligible (ὁ τῷ πάντα ποιεῖν), which Aristotle seems to exalt as the principal, separate, immortal, and eternal intellect (De an., III, 5, 430 a 10 ff.). Alexander of Aphrodisias, closer and more faithful to the Aristotelian text, understands the agent intellect as God himself, the first cause, who is the intellect par excellence (ὁ καὶ κυρίως κατὶ νόῳ; Alexander of Aphrodisias, De anima cum mantissa, ed. I. Bruns, Berlin 1887, p. 89, 18), whereas the possible intellect is called material (ὁλικός) and corruptible. Controversies concerning the intellect flourished in Arabic philosophy, in which the Neoplatonic tendency prevailed: for Avicenna, who continues the position of al-Fārābī, the separate intellect is the agent intellect and is posited as the last separate spiritual substance (in the emanative process), which infuses forms into material substances (dator formarum) and is the principle of knowledge for individual human beings. For his opponent Averroes, on the other hand, it is the possible or material intellect that is separate; it is one for the entire human species, eternal and incorruptible, and unites with individual human beings and particular phantasms through the cogitative power proper to each person (cf. Comm. in III De Anima, V, Venetian ed. 1562, fol. 138 ff.). The immense literary production of the late Middle Ages and the early Renaissance on the Averroist problem testifies to the lack of a sense of spiritual human interiority, against which St Thomas had already proclaimed his: hic homo intelligit (Sum. Theol., 1ª, q. 76, a. 1).
In modern philosophy the intellect follows the distinctive orientation of the various systems: in English empiricism the intellect (understanding) is reduced to a function of reflection upon the contents of experience; in pre-Kantian metaphysical rationalism, on the other hand, the intellect in various ways absorbs the cognitive value and functions of experience itself. Hegel would characterize this entire “metaphysics of the intellect” (Verstandesmetaphysik) as abstract and empty, especially in its later forms (Wolff). In Kant, the intellect is the faculty of the categories, whereas reason concerns itself with the Ideas (God, soul, world), which represent real totalities transcending the objectifying function proper to the categorial intellect. In Hegelian idealism, reason (Verund) completely prevails over the intellect (Verstand): every formality attained by the intellect is regarded as empty abstraction, and the series of formal perfections according to which the intellect conceives the scala entium is a “false infinity”; true reality is the dialectic of reason as the totality of the becoming of the human spirit and therefore the true Absolute (cf. Logik, 2nd ed. by A. Lasson, I, Berlin 1932, bk. I, sec. 1, chap. 1, p. 140 ff.; bk. III, sec. 3, chap. 3; Italian trans. by A. Mani, II, Bari 1925, p. 483 ff.). In more recent philosophy, the metaphysics of the intellect has been supplanted by the exaltation of science (empiricism, positivism...), by the “philosophy of life” and of “vital impetus” (Nietzsche, Bergson, Simmel...), and by the dialectic of existence and historical materialism. For St Thomas, the intellect has the function of apprehending the essence of things and the first principles both of speculative knowledge and of human morality (intellectus principiorum, syndereis), from which the movement of theoretical reason and the maturation of practical action begin (cf. Sum. Theol., 1ª, q. 79, aa. 8-12). V. CONCETTO; CONOSCENZA; GIUDIZIO; IDEA; INTELLETTUALISMO.