PREDICABLES. — The term (Gr. κατηγορούμενα, whence also in Italian «categorì») means «that which can be predicated» of another. In technical usage in logic, the p. are the «modes of predicability», that is, the general relations which predicates assume with respect to subjects. In Aristotelian realism, reality, conceived as an essential degree of being, open in its becoming to further modes and forms (accidents), grounds an ontological belonging of its own determinations. The p. indicate, expressed in a general logical relation, the degree and manner of belonging of all possible determinations of the real.
Aristotle (Topics, I, 4 [5]) distinguishes three classes of predicates: genus, property, and accident: «πᾶσα δὲ πρότασις...» γένος ἢ ἔδωσις ἢ συμβεβηκός δελτὶ».
The «property» (ἔδωσις) is then subdivided into χρυσός (not indicative of essence) and ζεός (definition, essence, species). The «difference» (διαφορά) is, in the passage cited, united with the genus by Aristotle, but elsewhere (Top., IV, ch. 6, 128 a 21 ff.) he affirms its distinction. The explicit classification into five p., genus, difference, species, property, and accident, is due to Porphyry (Isagoge, ch. 1); the same becomes common to Scholasticism: «omne quod de pluribus univoce praedicatur, vel est genus, vel species, vel differentia, vel accidens, vel proprium» (C. Gent., I, 32). It must be recognized that the foundation lies in the fact that a predicate either indicates determinately and adequately the specific nature of the subject (ζεός, species), or expresses it inadequately and indeterminately (γένος, genus), or indicates its essential distinctive note (διαφορά, differentia), or an attribute necessary and therefore derivable from the essence (δόξα, proprium), or finally a contingent and variable attribute (συμβεβηκός, accidens; cf. Aristotle, Top., I, 6 [8]). It is clear that the Aristotelian-Porphyrian classification, while it may be phenomenologically acceptable to other schools, insofar as its derivation and ontological justification are concerned, it functions within a substantialistic-pluralistic conception of the real. It therefore cannot have essential significance in phenomenism (v.), where the substantial structure of reality is denied, nor in monism (v.), which resolves the multiplicity of beings into a single substance or principle (v.). In Kant the p. are pure concepts of the understanding derivable immediately from the categories (e.g., «action and passion» from causality: cf. Kritik d. r. Vernunft, Transcend. Anal., I, 1, ch. 1, sect. 3, § 10; Italian trans. by G. Gentile, I, Bari 1940, pp. 113-14).
The genus is «that which is predicated essentially (ἐν τοῖς ἐστιν) of many things differing in species» (Aristotle, Top., I, 4 [5], 102 a 31). It is therefore an indeterminate essential predicate, such that, while it is found in all individuals of a class, it extends beyond it, e.g., «animal» said of man. It should be noted that the genus can be taken either in a «precissive» sense, excluding any further specific determination (purely abstract consideration), or in a «potential» sense without excluding its further possible determinations. It is in this second sense that the genus is predicated of species and of the individual: «man is a living being» does not exclude «what» kind of living being he is, but rather implicitly encloses it in the concreteness of the proposition. Hence, according to St. Thomas, the genus is predicated not as a part, but as a potential whole, inasmuch as «it implicitly includes in its signification, though indistinctly, the whole of which the species is determinately» (De ente et essentia, ch. 3; cf. C. Gent., I, 26). Since in the logical structure of reality different essential planes are determinable, the genera in which a subject may be placed are multiple (e.g., man is a living being, an animal, a vertebrate, etc.). The « proximate» genus, in relation to a given species, is that which immediately constitutes II. It must however be observed that the distinction of degrees or metaphysical planes is rightly held by the Thomist (cf. ibid.; In VII Met., lect. 12, n. 1564; Sum. Theol., 1, q. 76, a. 3 ad 4) as purely logical or formal-abstract: from the ontological point of view every nature or degree of being is unity and concreteness, even though, by reason of its real composition, it objectively grounds the notional fractionation into a scale of distinct concepts.
Difference is the essential distinctive predicate: it therefore indicates the specifically constitutive and characteristic element of a given nature, e.g., «rationality» in man. Difference is thus, in the proper sense, specific (speciem-faciens, ἐδόξας; Arist., Top., VI, ch. 6, 143 b 8). In Aristotle, however, the concept is still oscillating (cf. ibid., IV, ch. 6; Met., V, 9, 1018 a 12); and indeed in later logic the distinction of difference into «specific» and «generic» (the latter not constitutive of the species, since it determines a remote genus, e.g., «mortal» said of man) is accepted. Indeed, with Porphyry, Scholasticism accepts the distinction of difference into propriissimam, propriam, communem (the last purely accidental: cf. Sum. Theol., 1, 2, 2, q. 72, a. 5 c.; In Met., V, lect. 12, n. 916 ff.). The difference within the same species (individual difference) was called by the Scholastics «numerical» difference. The term is inexact, inasmuch as every individual realizes a different «perfection» and concretization of the species and is therefore constituted in its individuality by an ontological difference not merely quantitative-numerical. It should be noted that «difference» is not the same as «diversity»; for while the latter disregards it, difference always implies a community in the genus: «Differens omne est diversum sed non convertitur» (Thomas, In Met., loc. cit.; cf. Sum. Theol., 1, q. 3, a. 8 ad 3 and q. 90, a. 1 ad 3; C. Gent., I, 17).
Species is the complete essential predicate, said of many things differing in number (Porphyry, Isagoge, ch. 2). It therefore expresses the «ontological degree», the «essence», and also the «class» of the subject. Since the specific degree of a being is defined precisely as a determination of the genus, «species [and hence definition] result from genus and differences»: Ἐκ γὰρ τῶν γενῶν καὶ τῶν διαφορῶν τὰ εἴδη (Met., X, 7, 1057 b 7). The relation of species to genus (and analogously of the individual to species) is, according to Aristotle and St. Thomas, a relation of participation (v. cf. Arist., Topics, IV, 1, 121 a 12 ff; St. Thomas, In Boeth. De hebdom., lect. 2; C. Gent., I, 32, amplius 2). The derivation from Plato is evident, where the real-ideal form is imitated and participated in by empirical individual reality (v. IDEA). When identified with that of «class», the concept of species loses some of its ontological content, inasmuch as the «class» may be sufficiently qualified by common and constant characteristics, even if not essential, e.g., sometimes biological species or «classes».
Property indicates a predicate necessarily non-essentially, and causatum ex principiis essentialibus speciei (St. Thomas, De spiritualibus creat., a. 11, c.; cf. Aristotle, Top., I, 5, 102 a 31), e.g.: «man is capable of articulate speech». In the strict sense, therefore, property is a constant characteristic of an entire species and only of that species. But already by Porphyry (Isagoge, ch. 4; cf. Aristotle, Top., V, 1) «property» is understood in various senses: a) what belongs to one species but not to all; b) to an entire species but not only to that one; c) to an entire species, only to that one, but not constantly; d) to an entire species, only to that one, and always (omni, soli, semper). In the physical sciences and in natural history the concept of property is taken promiscuously in one or another of the indicated senses.
Accident is the contingent or variable predicate, that is, «which can be and not be without corruption of the subject» (Porphyry, Isagoge, ch. 5; cf. Aristotle, Top., I, 5 and 9; Met., IV, 30, 1025 a 14, 31), inasmuch as «it is not caused by the essential principles of the species, but happens to the individual» (St Thomas Aquinas, De spiritual. creat., a. 11, c.). For the most part, but not necessarily (ibid.; cf. J. Stuart Mill, System of logic, I, 1, ch. 7), accident denotes a character separable from the individual. It should be noted that the predicable accident is something other than accident in the metaphysical sense. The latter is defined in relation to substance as a determination (which does not belong to subsisting in itself) of subsistent being. Even what, from the standpoint of predicability or logical belonging, is proper may be, from the metaphysical standpoint, «accident», e.g., freedom in relation to spiritual substance. The metaphysical accident may further assume the determinations of genus and species: cf. the nine supreme genera of Aristotle’s classification of the categories (v.).
The Aristotelian-Scholastic doctrine of the predicables, as has been said, has objective foundation in experience, which attests to the multiplicity of degrees of being and the varying immediate ontological character of their determinations. It is not, however, free from limitations and uncertainties. J. Stuart Mill’s observation (v.) that genus may also be constituted by non-essential notions is well founded: e.g., the genus «biped» includes the biological species «man» (cf. System of logic, I, 7). As for specific difference, this may vary according to the type of classification intended: the naturalist, for example, seeks the «difference» of the human species in a direction other than rationality (in the subordinate morphological, physiological characters). The very concept of predicable is itself uncertain (already in Aristotle). It may indeed comprehend: a) the fundamental notes of a concept from which all others derive; b) the notes necessarily connected with those; c) the manifold essential relations of that concept. The distinction between what is «essential» or «specific» in the strict sense and what is «proper» is therefore not easy to make. «Essence», «species» are sometimes, more than concepts with a unitary ontological content, the result of a set of distinctive characters or «properties». Moreover, while classification serves fairly well for some fundamental divisions of natural entities (bodies, plants, animals, man), where logical determination proceeds by broad differences, it proves inadequate for the more concrete determinations of reality (it is almost impossible to determine the «difference» in mineral and biological species and subspecies). It is equally inadequate for artificial or logical-mental entities («essence» for artificial objects is an analogous concept, and therefore not every «specific» predicate is always strictly essential). Classification is even more difficult to apply where it is not a question of qualifying substances, but of facts, activities, phenomena, such as «movement», «energy», «mass», «electricity», «light» etc. (which play so large a part in the constitution and explanation of material reality), or «instinct», «need», «free act» (fundamental in biological-spiritual reality).
The Aristotelian-Scholastic predicables must therefore be understood as a mere logical approximation to the complex structure and articulation of reality.