INTELLECT. – It is the principle of the thought and consciousness of the human being that distinguishes man from lower forms of life.
The first affirmation of intellect as a supersensible activity is due to Anaxagoras (Aristotle, Met., I, 3, 984 b 15), who, however, limits himself to conceiving intellect (νόος) as the cause of the order of the cosmos and as the principle of motion and separation of things (H. Diels–W. Kranz, Die Fragmente der Vorsokratiker, II, 5th ed., Berlin 1935, B 13, p. 39). It is a matter of controversy whether Democritus admitted a distinction in nature between intellect and sense: it seems, however, that the fundamental principle of his theory of knowledge—that like is known by like (ἡμῶν ὁμολόγη)—is nothing other than the application of the common principle to the interaction of beings (cf. Aristotle, De gen. et corr., I, 7, 323 b 10 ff.). Deepened in its constitutive function for truth by Platonic idealism, 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): yet Aristotle left unresolved the problem of the personal individuality of intellect. Neoplatonism, in its attempt at a synthesis between Plato and Aristotle, conceived intellect as the second hypostasis between the One-Good and the Soul: Plotinus calls intellect the “first act of the Good” that revolves around the Good, while the Soul looks to intellect and through it arrives at God (Enn., I, 8; ed. E. Bréhier, I, Paris 1924, p. 116, 21 ff.). Plotinus and the entire Neoplatonic school strove to reconcile the separation posited by Plato between the δημιουργός and the παραδείγματα, yet no single theory has yet been found. In Proclus, who gathers the results of the tradition in a more systematic form, three degrees or moments of intellect are found: a) there is first a δεῖτον νοητὸν which is the principle of the intelligible and transcends it: τὸ νοητὸν κατ' αἰτίαν; b) next comes the νοῦς νοητὸς in which subject and object are εἰν κατ' αἰτίαν; c) finally there are the νόες participating, or κατὰ μέσες νοητὸς, 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 intellect, so to speak, forms the central theme of the historical development of Aristotelianism: the discussions will focus especially on 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 all things, and another that is like “cause and agent” (τὸ αἴτιον κατὰ ποιητικόν). There is therefore an intellect to which it belongs to become all things (ὁ νοῦς... τῷ παντὶ γίνεσθαι), and another to which it belongs to make all things intelligible (ὁ τῷ παντὶ ποιεῖν), which Aristotle seems to exalt as the principle, separate, immortal, and eternal (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 intellect par excellence (ὁ κατὰ κύριον ἐστὶ νοῦς; Alexander of Aphrodisias, De anima cum mantissa, ed. I. Bruns, Berlin 1887, p. 89, 18), while the possible intellect is said to be material (ὁ ἀληθής) and corruptible. The controversies over intellect flourished in Arabic philosophy, where the Neoplatonic trend prevailed: for Avicenna, who continues the position of al-Fārābī, the separate intellect is the agent intellect and is posited as the ultimate separated spiritual substance (in the emanative process) which infuses forms into material substances (dator formarum) and is the principle of knowledge for individual men. For his adversary Averroes, it is the possible or material intellect that is separate, unique for the entire human species, eternal and incorruptible, which unites with individual men and particular phantasms through the cogitative faculty proper to each (cf. Comm. in III De Anima, V, ed. veneta 1562, fol. 138 ff.). The immense literary production of the late Middle Ages and early Renaissance on the problem will be marked by the lack of a sense of human spiritual interiority, against which St. Thomas had already proclaimed: hic homo intelligit (Sum. Theol., 1a, q. 76, a. 1).
In modern philosophy, intellect follows the peculiar orientation of different systems: in English empiricism, intellect (understanding) is reduced to a function of reflection on the contents of experience; in metaphysical rationalism of the Kantian type, intellect in various ways absorbs the value and cognitive functions of experience itself. Hegel will qualify all this “metaphysics of intellect” (Verstandesphysik) as abstract and empty, especially in its later forms (Wolff). In Kant, intellect is the faculty of the categories, while reason concerns itself with the Ideas (God, soul, world) that represent real totalities transcending the objective function proper to categorical intellect. In Hegelian idealism, reason (Vernunft) completely takes precedence over intellect (Verstand): every formality attained by intellect is considered as empty abstraction, and the series of formal perfections by which intellect conceives the scala entium is “false infinity.” True reality is the dialectic of reason as the totality of the becoming of human spirit, and thus the true Absolute (cf. Logik, 2nd ed. by A. Lasson, I, Berlin 1932, I, 1, sect. 1, ch. 1, p. 140 ff.; I. III, sect. 3, ch. 3; Italian trans. by A. Mani, II, Bari 1925, p. 483 ff.). In more recent philosophy, the metaphysics of intellect has been supplanted by the exaltation of science (empiricism, positivism...), by the “philosophy of life” and of the “élan vital” (Nietzsche, Bergson, Simmel...), by the dialectic of existence and historical materialism.
For St. Thomas, intellect has the function of grasping the essence of things and the first principles both of speculative knowledge and of human morality (intellectus principiorum, synderesis), from which the movement of theoretical reason and the maturation of practical action begin (cf. Sum. Theol., 1a, q. 79, aa. 8–12). V. CONCEPT; KNOWLEDGE; JUDGMENT; IDEA; INTELLECTUALISM.