INDIVIDUATION, PRINCIPLE OF. — Existing beings in the world, while displaying an essential commonality in specific nature, are singular and individual: the principle of i. is that from which the individual determination of a nature or specific essence radically proceeds.
The search for the principle of i. has been a much-discussed problem in philosophy, especially in the medieval period. It “concerns the essential question of philosophy, and is not a mere subject of intellectual exercises, as the problems to which medieval philosophers devoted themselves are usually regarded” (G. Gentile, Teoria generale dello spirito, 4th ed., Florence 1924, p. 57). The problem, however, lost much of its importance in modern philosophy; Spinoza still deals with it, framing it within his pantheistic conception of reality, according to which the individual is nothing but a mode of the one divine substance. In his youthful Disputatio metaphysica de principio individui (1663), Leibniz resolves the problem in a nominalistic sense, simply affirming that each thing individuates itself (sua tota entitate individuatur). The problem is also briefly mentioned in Kant’s pre-critical period (Principiorum primorum cognitionis metaphysicae nova dilucidatio [1755]). With the rise of idealistic immanentism, the problem of the principle of i. loses the significance it had in the realistic conception of traditional philosophy, insofar as in idealism the plurality of individuals is absorbed into the unity of the transcendental Ego, although there remains an attempt to explain the multiplicity of the empirical world as dependent upon space and time. Schopenhauer had already explicitly placed the principle of i. in space and time: “for through time and space what is one and the same in being and in concept appears instead as different, as a juxtaposed and successive plurality” (Die Welt als Wille u. Vorstellung, I. II, § 23; Italian trans. by P. Savi Lopez and G. De Lorenzo, I, Bari 1928, p. 143 ff.). existentialism (v.) the problem of the principle of i. is considered rather from a psychological point of view, and its solution is indicated in the situation (parents, homeland, period, etc.) through which each person is inserted into reality and from which he receives his individuation. Philosophically, however, the ontological aspect of the problem is more important—so obscure and difficult that Bossuet almost despaired of being able to resolve it (La logique, chap. 23).
In order to assess the various solutions more adequately, it is useful to distinguish the various ways in which the principle of i. may be understood. First of all, it may serve as a merely manifestative principle of i.: as such, it consists in that complex of qualities by which the various individuals are empirically distinguished; for example, in the case of man: first name, surname, paternity, place and date of birth, more or less profound somatic characteristics such as stature, features, colour (of the eyes and hair), timbre of the voice, and fingerprints. This complex of determinations is generally sufficient to distinguish two living beings of the same species (although not always, as, for example, in some cases involving twins). It is no easier to determine the distinctive characteristic features of individuality in inorganic beings, for example, in two molecules of water. Yet these too are individually distinct, and therefore presuppose a constitutive principle of their individuality.
In the search for the constitutive principle of i., the efficient cause from which every effect receives its singular reality and hence its individuality has sometimes been indicated. It must be observed, however, that the efficient cause, being extrinsic to the effect, is only its extrinsic principle of i.; the problem concerning the intrinsic principle of i. consequently remains unresolved, since every being must have within itself (even if received from the cause) the reason for its own individuality. Nor can this intrinsic principle of i. be understood as the complete essence of the individual thing (F. Suárez, Disp. Met., d. 5, s. 6), since it is precisely the principle of this individuality that is being sought; nor can it be understood as something really
distinct from it (the haecceitas of Scotus: In I Sent., 2, d. 3, q. 6), because every thing is essentially singular or individual, and therefore the intrinsic principle of i. must be found in its very essence.
Aristotelian-Thomistic metaphysics (Aristotle, Met., XI, 8; St. Thomas, De ente et essentia, chap. 2) identifies matter as the intrinsic constitutive principle of the i. of bodies. Certainly spiritual substances too are individual; but for them the problem does not arise because, according to the Aristotelian-Thomistic principles of the limitation and multiplication of act through potency (v. ATTO E POTENZA), spiritual essences, not received in a potency, cannot be multiplied within the same species, but are individual in themselves; every individual is therefore a species, and individuation coincides with specification. This applies all the more to God, whose essence, being identified with the pure act of being, is absolutely unchangeable and therefore individual and singular in itself. The problem is thus confined to material substances (and accidents), which admit a multiplicity of individuals within the same species. According to St. Thomas, this multiplicity is possible insofar as act, that is, specific perfection, is received in a potency or subject—namely, in matter (accidental act in substance)—and is multiplied and individuated according to the multiplication and individuation of matter. Thus, whereas specification comes from act, that is, from form (man is such by virtue of the soul), individuation comes from matter (he is “this” man by virtue of matter).
Matter, however, is not a principle of i. insofar as it is prime matter or pure potentiality, but insofar as it is endowed with quantity; for matter without quantity has no extension and therefore has no parts; it is neither this nor that, that is, it is not individual and consequently cannot individuate form or act. By virtue of quantity, on the other hand, matter is extended and consequently has parts that are distinguished from one another by the different position they occupy in space (ex situ); they are “this” or “that,” that is, individual, and can therefore individuate form. Thus this material substance is “this individual” because it has this essence, composed of this matter and this form; and the form is “this” because it is received in this matter, which is “this” because it is this determinate part within the totality of corporeal matter; “designated matter” is therefore the intrinsic constitutive principle of i. of corporeal substances.
Intorno alla « materia signata » si fa questione fra gli scolastici, se la « signatio » o individualizzazione della materia sia dovuta all'ordine che essa dice alla quantità o alla quantità stessa attualmente informante la materia. Il problema deriva dal fatto che la materia non può essere informata dalla quantità se non ha il proprio atto o forma sostanziale, previo ad ogni accidente; d'altra parte la materia non può individuare la forma se non è essa stessa individua; donde concludono alcuni scolastici con il Gaetano (Comment. in De ente et essentia s. Th. Aq., cap. 2) che dovendo la materia essere individua prima di ricevere la quantità per potere individuare la forma stessa, l'individuazione della materia si ha non per la quantità attualmente informante la materia, ma per l'« ordine » alla quantità che è nella materia prima della quantità stessa. Ma giustamente osservano altri con il Ferrarese (Comment. in Sum. c. Gent. I, 21) e secondo la sentenza del Capreolo (Defens. theol. d. Th. Aq., t. III, ed. C. Paban & Th. Pègues, Tours 1902, p. 200 sgg.) che la priorità della forma sostanziale rispetto alla forma accidentale o quantità è priorità di natura, non di tempo, per cui nello stesso istante si hanno materia, forma e quantità che insieme concorrono a costituire il nuovo ente: la forma specificando, la quantità segnando la materia, e la materia limitando e individuando la forma.
Alla soluzione indicata non fa difficoltà l'anima dell'uomo che, essendo immortale, sussiste, dopo la morte, individua e singolare, pur non essendo unita alla materia. Infatti l'anima umana, in quanto spirituale, ha l'essere indipendente dal corpo e perciò, pur creata nel corpo e da esso individuata, come conserva il proprio essere sussistente, così conserva la propria individuazione, rimanendo sempre tale forma pronta a ricostituire quello stesso.
individuo, quando (la filosofia lo ignora, ma la fede lo insegna) si ricongiungerà con il corpo nella finale Risurrezione.