IDEA. - The term, of Greek origin (ἰδία and εἶδος, from ἰδεῖν, to see), indicates, in its primitive reference, figure, visible aspect, form: ἰδεῖν τῆς γῆς (Plato, Phaed., 108 d; the same meaning in Aristotle, Hist. animal., VI, 35, 580 a 28). The Latin species corresponds to it (from spectare, to look at; Cicero placed the term forma before it: Top., 7, 30; but already in his time the Greek word had entered Latin without undergoing changes). It is perhaps from the value that the exterior figure has as sign and expression of the internal structure of beings that the term could be transferred to indicate the "form" or essential "type" of things. This is the fundamental metaphysical-logical meaning that the term (already used by Democritus in the sense of "determination" and "schema": ἰδεῖν or σχήματα as atomic structures of matter) assumed in Plato and then, with a variety of applications, in the philosophical currents connected with Platonism. In the history of philosophical thought the term was then overloaded, as few others, with further meanings and systematic references.
The i. is in Plato the intelligible unity of the many (Resp., VI, 507 b); the i. subsist for themselves, immutable, ungenerated, incorruptible (Tim., 51 d ff.); incorporeal, they are the true essence (τὴν ἀληθινὴν οὐσίαν, Soph., 246 b); the reasons and the truth of beings (τῶν ὄντων τὴν ἀλήθειαν, Phaed., 99 e); the exemplars of nature (παραδείγματα ἐν τῇ φύσει), to which all other things are similar and insofar as such participate (Parm., 132 d). The i. therefore has value in the Platonic system as the rational principle and value of things, their essential determination, and is at the same time the object of intuition or vision (in this there is perhaps another justification of the Platonic use of the term) of the soul. The i. not only have ontological value but, in the interpretation that Aristotle gave of them, subsist in themselves, outside of material and visible reality (cf. Met., I, 6, 9; XI, 1, 4; VI, 14; XII, 9; XIII, 4). Aristotle, while denying such separate subsistence (ibid., VI, 13), preserves the metaphysical value of the i. The εἶδος (μορφή, οὐσία δεύτερα) is in fact the universal, the one and the same in the many (ἐν καὶ αὐτὸ ἐπὶ πλεόνων: Analyt. post., I, 11, 77 a 9) and namely the essential unity common to all individuals, which is real only in them and derives from them: ἐκ τῶν καθ' ἕκαστα γὰρ τὸ καθόλου (Eth. nicom., VI, 12, 1143 b 4): the i. therefore is not, as in Plato, the object of intuition but is obtained through an abstractive process.
In the Platonic-Aristotelian tradition, ancient and medieval thought is for the most part maintained. The Stoics, while reducing the i. as general concepts to a purely subjective-empirical value (they are the simple persistence of sensible representations: an anticipation of Hume), nevertheless admit a rational principle (λόγος σπερματικός) immanent in nature. Similarly Philo, who places within things the "rational powers" (δυνάμεις λόγοι) and sees in the i. and supreme force (the Λόγος) the exemplary form of the world (cf. De mundi opificio, 17 ff., 24-25). For Cicero the i. are, as already in Plato, "formae rerum", exemplary principles belonging to the purely intelligible order ("cogitatione tantum et mente complectimur" [ideas]), ungenerated, immutable, eternal (De orat., ch. 3). Similarly Seneca: "Idea est eorum quae natura fiunt exemplar aeternum" (Epist., 58).
In Plotinus the i. are the eternal content of the spiritual act (νοῦς) with which they are identified. They constitute the intelligible world (κόσμος νοητός) of the spirit; and since activity and thought reside as "its own force" in being, the i. are "the form of being and its operative force" (Enn., V, I, 9, ch. 8-9). For St. Augustine (and the thought of Pseudo-Dionysius is analogous: cf. De div. nom., ch. 5) the i. are the "rationes aeternae" existing in God, form and exemplary cause of all created things:
"ideae principales quaedam formae vel rationes rerum stabiles atque incommutabiles... quae in divina intelligentia continentur" (Quaest. 83, q. 46: Pl. 40, 30): eternal and absolute values, the i. transcend, as immutable objectivity, individual human consciousnesses (De lib. arb., III, 7). In God they have value as formal determinations of his infinite truth: to participate therefore in the i. implies in human knowledge the actualization of a relationship with absolute truth and therefore with God (cf. De Civ. Dei, XI, 10).
In the early Middle Ages the Platonic conception of the real subsistence of the i. is taken up again with regard to the problem of universals (v.). The "species" has, for William of Champeaux, true consistency of substance and is found again, as an ontological unity (not merely formal), in the multiplicity of individuals (cf. Abelard, Hist. calamitatum, ch. 2). The further discussion of the problem of universals led to the more mature formulation of the i. as form pre-existing in God (universal "ante rem"), as reality individuated in single beings (universal "in re") and as universalization operated by the mind of the specific unity of individuals (universal "post rem"); cf. St. Thomas, De ente et essentia, ch. 4; Quodlib., q. VIII, a. 1). But more than of i., in the problem of universals one spoke of "species", "conceptio", "genus". In the great medieval theologians the term i. rather preserves the metaphysical, Neoplatonic-Augustinian meaning of exemplary cause and form in the divine mind. For St. Albert the Great the i. are "in mente divina secundum quod ars est omnium creatorum" (Sum. Theol., 1ª, q. 55, a. 2). According to St. Bonaventure "ideae rerum ante mundi constitutionem in mente Creatoris erant" (Comp. Theol., I, 25). This doctrine is developed by St. Thomas: "oportet dicere quod in divina sapientia sint rationes omnium rerum quas... diximus ideas; id est formas exemplares in mente divina exsistentes" (Sum. Theol., 1ª, q. 44, a. 3, c.; cf. q. 15, a. 1, c.). The i. in general is form, that is, the objective expression of a thing: it has the function of exemplary principle insofar as it directs action: of cognitive principle insofar as it is the term by which the thing is given in consciousness, "secundum quod formae cognoscibilium dicuntur esse in cognoscente" (ibid.). In both senses the i. are in God: as principle of creative activity the i. in the divine mind is "exemplar"; as principle in which and through which the divine knowledge of things is actualized, the i. is "ratio" (ibid., n. 3).
The second of the two senses indicated in St. Thomas (the i. as cognitive representation) is already close, albeit with a different gnoseological meaning, to the modern sense which arrives (in antithesis to the Platonic meaning for which the i. was an objective reality in itself) at the identification of the i. with "mental representation," distinguished from reality in itself. In Descartes the i. is in fact, in a technical sense, "the form by which every thought or content of knowledge is immediately given to consciousness": "ideae nomine intelligo cuiuslibet cogitationis formam per cuius immediatam perceptionem eiusdem cogitationis conscius sum" (Risp. alle II obiez., definiz., 2). The i. is, that is, the immediate mental form and term by which every content (intelligible-sensible) is given. Such content, insofar as it is in the i., is called by Descartes the objective reality of the i. (ibid., 3). Thus the i., by itself, does not at all put thought in contact with the real in itself, but rather encloses it within the intentional sphere of representation (cf. Med., III). This concept of the i., which is at the basis of the gnoseological immanentism of modern philosophy and from which the modern sense of idealism (v.) is in part derived, is found again in Malebranche (the i. is the immediate object of the spirit; that which is given in the representative sphere of consciousness); in Spinoza (the i. is the conception of the mind insofar as it is a thinking substance: "per ideam intelligo mentis conceptum quem mens format propterea quod est res cogitans" (Eth., II, def. 3). The i. constitute the objective being of things, existing as a "nexus of causes" in the infinite divine i.: ibid., prop. VIII, XX); in Leibniz (the i. is a form pre-existing in God and in our intellect, nor does it by itself import the real existence of that which it represents: Nov. Est., III, ch. 4, § 2). The value of the i. as a pure mental image is also a fundamental conception of empiricism. In Locke the i. is any object of knowledge and of thought. The i. therefore embraces all the contents of consciousness, whether representative (sensations, images, concepts) or affective (feelings). Only in the i. does the immediate object of thought consist. This principle becomes rigorous immaterialism in Berkeley; i. are all the objects of our knowledge (Principles, § 25); and since the i. exist only in the spirit (ibid., § 22), any sensible representation of ours cannot objectify itself in a material reality existing for itself. Things coincide with the i.; empirical reality is nothing but the order and constant succession of the i., impressed upon our spirit by God (ibid., §§ 33-39). Hume, preserving and indeed accentuating the purely immanent meaning of states of consciousness, understands by i. the images or representations derived from the original states of consciousness, that is, from impressions (Treatise, I, sec. 1, § 1). The difference between i. and impressions lies in the different degree of vividness and force: the i. are nothing but the faint reflection ("faint images") of impressions. Rationalism and empiricism therefore operate, in the same direction of immanence, the reduction of the contents of consciousness, the former absorbing into the i. as rational value the concreteness of experience, the latter dissolving into the i. as sensible representation, or associative synthesis of sensible representations, the intellectual-rational values and concepts.
In Kant the i. assumes a new technical meaning. It is, that is, an a priori representation or transcendental concept of reason, which is not referable to the phenomena of experience as their form or category, but holds only as the ideal term of the whole totality of experience: "I understand by i. a necessary concept of reason to which no adequate object can be found in the senses" (Critica della r. pura; Dialettica trasc., sec. 2; Ital. trans. by G. Gentile and G. Lombardo Radice, I, Bari 1940, p. 300). The i., and in the first place the three fundamental ones (world, I, God), hold only as pure ideal limits or terms of convergence of experience in the absolute.
In post-Kantian idealist immanentism the i. assumes a metaphysical value even more universal than that which it had in Platonism. With every pluralism and dualism abolished, the i. becomes the objective force of the spirit that unfolds, as reason, in the world, and therefore is understood as the true substance and the transcendental unity in which all the moments of the real are resolved. Such absolute valorization of the i., already present in Schelling ("i. is the synthesis of the absolute identity of the universal and the particular"; "nature is a reflection of the i."), is developed in the Hegelian system. For Hegel the i. is "the adequate concept, the true objective, that is, the true as such. When something has truth, it has it through its i., that is, something has truth only insofar as it is i." (La scienza della logica, Ital. trans. by A. Moni, III, Bari 1927, sec. III, p. 242). "Being has reached the meaning of truth insofar as the i. is the unity of the concept and of reality; it is therefore henceforth only that which is i." (ibid., p. 246). It should be noted that for Hegel "the identity of the i. with itself is one and the same as the process" (ibid., p. 248), that is, the i. is in its innermost being dialectical. Consequently in every moment of the real, by virtue of its immanence in the i., the profound meaning of identity dominates. To idealism should be brought near Schopenhauer, for whom the i. indicates the immutable degrees of the objectification of the will, that is, of its phenomenal unfolding in the world and in multiplicity: "These degrees stand to individual objects as their eternal forms and their models" (Il mondo come volontà e rappresentazione, I, Ital. trans. by P. Savj-Lopez and G. De Lorenzo, Bari 1928, bk. II, § 25, pp. 162-63).
After idealism, not to speak of substantially traditional attitudes (for example, Rosmini, in whom the i. "is properly the intelligibility of essences, or, which is the same, their objectivity," and that is, in the end, their value of being: Teosofia, V, ed. naz., Rome 1939, p. 127, 136), one must note the conception of Kantian inspiration, which understands the i. as pure theoretical values, in themselves devoid of ontological content: idealities into which the subject pours itself and which therefore place themselves on the horizon of the spirit as term and aim of realization in the process of thought and of action (e.g., H. Rickert: cf. System d. Philos., I, Tübingen 1921, p. 158 ff.).
But the negation of the metaphysical value of the i. has found its most systematic expression in the recent forms of irrationalism (Scheler, Sprenger, Stirner, Nietzsche, Marxism, existentialism) which represent in contemporary philosophy the most decided detachment from the tradition of Greek-Christian-modern idealism. Already in Feuerbach the i. is "abstraction," "unreality," "theological phantom" in the face of the one firm reality of nature. A concept that has assumed, as is well known, ample theorization in Marxism, for which the only true dialectic is the naturalistic-economic process of the world: of such a process consciousness and particularly the i. (understood as doctrines, theories, values, ideologies) are a simple reflection and therefore mutable, in function of the same cosmic becoming. In today's forms of existentialism, in opposition to the i. as universal intelligible value, the alogical existential categories assume absolute pre-eminence as revealing and constitutive moments of spiritual reality: singularity, possibility, decision, freedom, situation, temporality, risk, death, etc.
In neo-Scholastic philosophy the use of i. as an intellectual notion or representation has sometimes been restored, distinguished, by its characters of universality and necessity, from the concrete-particular sensitive representation. But there is now a tendency, opportunely, to prefer in this sense the term concept (v.), less burdened with secondary meanings.
Referring to the entry IDEALISM for the fundamental theoretical problems concerning the idea in its metaphysical reference, one may note the objective foundation inherent in the various historical meanings of the term, on which its wide use in current language also depends.
The ontological meaning (Plato, Aristotle, Plotinus, St. Augustine, St. Thomas and, in a general sense, idealism) is justified by the reflection that a determination or essentiality in being outside thought is not possible, and therefore every meaning and sense of reality must be traced back to a rational principle. In this sense, and referred to the absolute plane of reality, the principle formulated by Hegel holds that "everything real is rational." The expression "ideas rule and move the world," beyond its more immediate sense (doctrines, theories, systems, opinions determine action: cf. the "idea-forces" of A. Fouillée), also has the profound meaning (essential in a theistic-transcendent conception) that reality is, in its becoming, the actualization of a rational value that constitutes at once the ontological nature of beings and posits itself as the teleological term of their operation.
The idea in the sense of "model" or directive "exemplar" of action (the current expression "a man of ideas" refers to this) is connected to the predetermination of the end proper to spiritual volitional activity: "Haec ergo videtur esse ratio ideae, quod idea sit forma quam aliquid imitatur ex intentione agentis, qui determinat sibi finem" (St. Thomas, De verit., q. 3, a. 1; cf. the entire question).
The meaning of idea as mental representation, content of thought distinguished from reality (current language refers to this in these and similar expressions: "association of ideas"; "to have no idea of a fact, a place, a person"; "it is only an idea") finds an explanation and justification in the fact that the idea, as subjective form of knowing (the "species" or "verbum mentale" of scholastic terminology), has no existence except in the knowing subject; it can therefore and must, in this sense, be contrasted with reality in itself which, when gnoseological transcendence is involved, cannot in its real being become the immediate term of knowing. There is furthermore a justification in the fact that the spirit has the power to produce representations without correspondence in ontic reality, for example, in dreams, in imagination. But this does not imply the general assumption that the idea cannot transcend itself as subjectivity, nor be, as regards its objective content, an immediate reference to the real. The purely subjective value of the idea is a systematic postulate of gnoseological immanentism, in no way validated by experience. Mental representation is in fact not to be understood, in itself, as the object and term of the cognitive act, but rather as the intentional mediation by which consciousness relates itself to the real on the various planes of its objectivity. The idea is precisely the effective positing in consciousness of this relationship. At the basis of the Cartesian-Lockean assumption there is the radical error of having suppressed or ignored the profound discriminations that experience imposes among the different forms and moments of knowing and the corresponding gradation of ontic-existential consistency of the contents of consciousness. Having denied the objective reference of the idea in order to consider it only in its subjectivity was logically bound to lead to the absolutization of the I as subject and ultimately as pure act. The actualism of G. Gentile (v.) has precisely absorbed into the spirit as act any residue of objectivity that even in post-Kantian idealism was still recognized in the idea.
Further acceptations of the term in current usage (idea as intention, purpose, opinion, etc.) tend to dissolve its systematic meaning. By contrast, the substantivization, frequent in Italian, of the term "ideal" is linked back to Plato, as is the acceptation of idea as the part or essential nucleus of a system, a doctrine: "the religious idea," "the Christian idea."