PREDICABLES. — The term (Gr. κατηγορούμενα, whence also, in Italian, “categoremes”) means “that which can be predicated” of something else. In its technical sense in logic, p. are the “modes of predicability,” that is, the general relations that predicates assume toward subjects. In Aristotelian realism, reality, conceived as an essential degree of being, open, in becoming, to further modes and forms (accidents), grounds a distinct ontological belonging of its own determinations. P. indicate, expressed in a general logical relation, the degree and mode of belonging of all possible determinations of the real.
Aristotle (Topica, I, 4 [5]) distinguishes three classes of predicates: genus, proprium, and accident: « πᾶσα δὲ πρότασις... ἢ γένος ἢ ἴδιον ἢ συμβεβηκός δελοί ».
The “proprium” is then divided into ἴδιον (not indicative of the essence) and ὄρος (definition, essence, species). “Difference” (διαφορά) is joined by Aristotle to genus in the passage cited, but elsewhere (Top., IV, chap. 6, 128 a 21 agg.) he asserts its distinction. The explicit classification into five p.—genus, difference, species, proprium, accident—is due to Porphyry (Isagoge, chap. 1); it subsequently became common in scholasticism: « omne quod de pluribus univoce praedicatur, vel est genus, vel species, vel differentia, vel accidens, vel proprium » (C. Gent., I, 32). Its foundation must be recognized in the fact that a predicate either indicates the specific nature of the subject determinately and adequately (ὄρος, species), or expresses it inadequately and indeterminately (γένιος, genus), or indicates its essential distinguishing note (διαφορά, differentia), or a necessary attribute and therefore one derivable from the essence (ἴδιον, proprium), or finally a contingent and variable attribute (συμβεβηκός, accidens; cf. Aristotle, Top., I, 6 [8]). It is clear that the Aristotelian-Porphyrian classification, although phenomenologically it may also be accepted by other schools, is, as regards its derivation and ontological justification, a function of a substantialist-pluralistic conception of the real. It therefore cannot have essential significance in phenomenalism (v.), where the substantial structure of reality is denied, monism (v.), which resolves the multiplicity of beings principle (v.). In Kant, p. are pure concepts of the understanding immediately derivable from the categories (e.g., “action and passion” from causality: cf. Kritik d. r. Vernunft, Transzend. Anal., I, I, chap. 1, sect. 3ª, § 10; Italian trans. by G. Gentile, I, Bari 1940, pp. 113–14).
Genus is “that which is predicated essentially (ἐν τῷ τι ἄστιν) of many things differing in species” (Aristotle, Top., I, 4 [5], 102 a 31). It is therefore an indeterminate essential predicate, that is, one which, although found in all the individuals of a class, extends beyond it—for example, “animal” said of man. It should be noted that genus may be taken either in a “precisive” sense, excluding every further specific determination (a purely abstract consideration), or in a “potential” sense, without excluding its further possible determinations. It is in this second sense that genus is predicated of species and individual: “man is a living being” does not exclude “which” determinate living being he is; indeed, in the concreteness of the proposition it implicitly includes II. Hence, according to St. Thomas, genus is predicated not as a part but as a potential whole, since « implicite in sua significazione, quamvis indistincte, totum id quod determinate est in specie dicit » (De ente et essentia, chap. 3; cf. C. Gent., I, 26). Since different essential levels can be determined in the logical structure of reality, the genera in which a subject can be placed are numerous (e.g., man is living, animal, vertebrate, etc.). “Proximate” genus, in relation to a given species, is that which immediately constitutes II. It should nevertheless be observed that the distinction of metaphysical degrees or levels is rightly regarded by Thomism (cf. ibid.; In VII Met., lect. 12, n. 1564; Sum. Theol., 1ª, q. 76, a. 3 ad 4) as purely logical or formally 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 noetic division 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, properly speaking, specific (speciem-faciens, εἰδοποιός; Arist., Top., VI, chap. 6, 143 b 8). In Aristotle, however, the concept is still fluctuating (cf. ibid., IV, chap. 6; Met., V, 9, 1018 a 12);
and, moreover, in later logic the distinction between “specific” and “generic” difference is accepted—the latter not constituting the species, inasmuch as it determines a remote genus, e.g., “mortal” said of man. Indeed, with Porphyry scholasticism accepts the division of difference into propriissimam, propriam, communem (the last being purely accidental: cf. Sum. Theol., 1ª-2ª, q. 72, a. 3 c.; In Met., V, lect. 12ª, n. 916 agg.). Difference within the same species (individual difference) was called by the scholastics “numerical” difference. The term is inaccurate, since every individual realizes a different “perfection” and concretization of the species and is therefore constituted in its individuality by an ontological difference that is not merely quantitative and numerical. It should be noted that “difference” is not the same as “diversity”; for, whereas the latter abstracts from it, difference always implies a commonality in genus: « Differens omne est diversum sed non convertitur » (St. Thomas, In Met., loc. cit.; cf. Sum. Theol., 1ª, 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 numerically “(Porphyry, Isagoge, chap. 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 genus, “species [and therefore definition] result from genus and differences”: Ἐκ γὰρ τοῦ γένους καὶ τῶν διαφορῶν τὰ εἶδη (Met., X, 7, 1057 b 7). The relation of species to genus (and, analogously, of individual to species) is, according to Aristotle and St. Thomas, a relation of participation (v. cf. Arist., Topica, IV, 1, 121 a 12 agg; St. Thomas, In Boeth. De hebdom., lect. 2ª; C. Gent., I, 32, amplius 2). Its derivation from Plato is evident, where εἶδης is the real-ideal form, 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, since a “class” may be sufficiently characterized by common and constant features, even if they are not essential, as, for example, biological species or “classes” sometimes are.
The proprium indicates a predicate necessarily connected with the specific nature, « 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 expressive articulated speech.” In the strict sense, proprium is therefore a constant characteristic of an entire species and of that species alone. But already in Porphyry (Isagoge, chap. 4; cf. Aristotle, Top., V, 1), “proprium” is understood in different senses: that which belongs a) to one species alone but not to the whole of it; b) to an entire species but not to that species alone; c) to an entire species and to that species alone but not constantly; d) to an entire species, to that species alone, and always (omni, soli, semper). In the physical sciences and in natural history, the concept of proprium is used indiscriminately in one or another of the senses indicated.
Accident is the contingent or variable predicate, that is, “which may be and not be without corruption of the subject” (Porphyry, Isagoge, chap. 5; cf. Aristotle, Top., I, 5 and 9; Met., IV, 30, 1025 a 14, 31), insofar as “non causatur ex principiis essentialibus speciei, sed accidit individuo” (St. Thomas, De spiritual. creat., a. 11, c.). For the most part, though not necessarily (ibid.; cf. J. Stuart Mill, System of logic, I, I, chap. 7), accident indicates a character separable from the individual. It should be noted that the predicable accident is something different from accident in the metaphysical sense. The latter is defined in relation to substance as a determination (to which subsisting in itself does not belong) of the subsistent being. Even that which, from the standpoint of predicability or logical belonging, is “proper,” may, from the metaphysical standpoint, be an “accident,” e.g., freedom in relation to spiritual substance. Accident in the metaphysical sense may furthermore assume the determinations of genus and species: cf. the nine supreme genera of the Aristotelian classification of the categories (v.).
The Aristotelian-scholastic doctrine of the p., as has been said, has an objective foundation in experience, which attests to the plurality of the degrees of being and to the varying ontological immediacy of their determinations. It is not, however, free from limitations and uncertainties. The observation of J. MELLO (v.), for example, is well founded: genus may also be constituted by non-essential notions, e.g., the genus “biped,” including the biological species “man” (cf. System of logic, I, 7). As for specific difference, it may vary according to the type of classification intended: the naturalist, for example, seeks the “difference” of the human species in a direction different from “rationalitas” (in somatic, morphological, and physiological characteristics). The concept of an “essential” predicate itself is (already in Aristotle himself) uncertain. It may in fact include: a) the fundamental notes of a concept from which all the others derive; b) the notes “necessarily” connected with them; c) the multiple essential relations of that concept. It is therefore not easy to distinguish what is “essential” or “specific” in the strict sense from what is “proper.” “Essence” and “species” are at times, rather than concepts with a unitary ontological content, the resultant of a set of “distinctive characteristics” or “properties.” Moreover, if classification serves fairly well for certain fundamental divisions of natural beings (bodies, plants, animals, man), where logical determination proceeds by major differences, it proves inadequate for the more concrete determinations of reality (it is virtually impossible to determine the “difference” in mineral and biological species and subspecies). It is equally inadequate for artificial or logical-mental entities (“essence” with regard to artificial objects is an analogous concept, and therefore not every “specific” predicate is always essential in the strict sense). Classification finds still more difficult application when the matter is not the qualification of substances but of facts, activities, and phenomena, such as “movement,” “energy,” “mass,” “electricity,” “light,” etc. (which play so large a part in the constitution and explication of material reality), or “instinct,” “need,” and “free act” (fundamental in bio-spiritual reality).
The Aristotelian-scholastic p. must therefore be understood as a merely approximate logical approach to the complex structure and articulation of the real.