CATEGORY. - Originally it was the "accusation," that is, the judicial action opposed to "apology," according to Aristotle (Rhet., I, 3, 1358b 11), who appears to have been the first to use the term "c." in a strictly philosophical sense, so as to make it the object of the first treatise of the Organon. Categories are the meanings that the terms of judgment have when they are used alone "without any synthesis," such as "man," "horse," "runs," "wins"; they are therefore the most characteristic "indications and determinations" of language, thought and reality: not exclusively "predicates," because Aristotle counts among the categories — indeed places first — the singular substance, that is, the ultimate subject (Met., IX, 1, 1042 a 26). In fact Boethius rendered the Greek term not with praedicatum, "predicate," but with praedicamentum, which is what in some way enters into a predication either as subject or as predicate; it is therefore vain to criticize, as some moderns do (N. Hartmann), the Aristotelian notion by alleging that not all categories are "predicates." According to David the Armenian, the categories are the meanings of "first position" (Scholia, 29 b 21), namely: substance, quantity, quality, relation, action, passion, place, time, position and state. But this does not appear to be a fixed number, since, while the earlier works give the complete list (Cat., 4, 1 b 25; Top., I, 9, 103 b 20), the more mature works give lists varying from a maximum of eight (Met., XII, 12, 1068 a 8) down to six, five, four or only three (see H. Bonitz, Index Ar., 378 a 49 ff.). The order too is not constant, except for substance, which always holds the place of honor. Hence also the root or the pretext of the arduous controversies that have tormented Aristotelians of every age. First of all, the question is asked whether the categorical list is to be taken as a classification of mere words, "φωναί" (Alexander of Aphrodisias, Eustathius and the nominalists), or of mere concepts, "νοήματα" (Herminus, the conceptualists), or of mere things, "πράγματα" (Plotinus, Porphyry, the Stoics, the ontologists). David, to whom we owe the report (Scholia, 28 b 7 ff.), prudently sees the three solutions as mutually connected moments of the single interpretation that adequately renders the character and fullness of Aristotelian realism: the categories are "simple words which signify simple realities by means of simple concepts" (op. cit., 29 b 25). Trendelenburg, while recognizing their metaphysical significance, maintained that the first derivation of the Aristotelian categories is purely grammatical: the first four correspond to nouns with adjectives and numerals, the last four to verbs, and the two in the middle to adverbs. An ingenious hypothesis, and one that undoubtedly contains a part of truth, but which lacks direct confirmation in the Aristotelian texts, where the derivation of the categories always has a purely theoretical framing, and must therefore refer back to metaphysics (Bonitz, Brentano, Ragnisco, Ross, together with the realists of the school).
The categories refer back to and relate to "being," of which they express, first through concepts and then through words, the different forms accessible in experience. Also foreign, therefore, to Aristotle's mind is O. Apelt's attempt to see in the categories the "formal functions" that the "is" exercises as copula of judgment: an exegesis constantly contradicted, moreover, by the texts that sharply distinguish the two meanings, logical and real (see: Met., V, 7, 1017 a 8 ff.; X, 10, 1051 a 35 ff., etc.). One must hold to the strong Aristotelian expression "categories of being," "genera of being," and to the declaration that "as many are the ways in which being is said, so many are its meanings" (Met., V, 7, loc. cit.). The categories are "genera," that is, conceptual determinations of minimal content that cannot be further resolved, but into which all the others of denser content within their own sphere are resolved, as can well be observed by traversing Porphyry's tree from bottom to top. Moreover they are called categories and genera of "being," and by this is indicated both the content and the principle of division. The categories classify real being and not the mental concepts of being, the predicables. But since they classify it in its defined, and therefore limited and univocal, form, they are no less distinguished from the divisions that belong to being in the breadth of analogy: finite and infinite, act and potency, essence and existence... Between this essentially ontological division and the purely logical one of the predicables (v.) stands the division of the categories, which thus participates in the nature of both and can consequently serve as mediator between the one and the other. And since, for Aristotle, the forms of being and their actual connection precede and ground the apprehension and connection that the mind makes of them, this mediation or ambivalence of the categorical classification ensures at one and the same time the rational character of his metaphysics and the realistic background of his logic. Having as its content and principle of derivation real being, that is, the composite of essence and act of being, the derivation expresses the mode according to which a real nature comes to have the act of being: that nature which has enough consistency to be able to have the act of being directly in itself, and is therefore a subsistent subject, is substance (v.); what instead can only be "in another," as a modification of the nature of that same thing, is accident; accidents are then further divided according to the nature and the modalities of this belonging to substance. The attempts, therefore, to place at the center of the classification either movement (Bröcker), or relation (Zeller), or pure "essence" as such (N. Hartmann), remain outside Aristotelian-Thomistic realism.
Since the categories must express the economy of thought in determining reality with respect to mutable and manifold experience, the meaning and determination of the categories themselves depends on the concept of reality that a philosophy assumes at its starting point. Hence in philosophies for which being is "given" and offered to the contemplating mind (objectivism), the categories are determinations of being before they are of thought, and qualify thought only in dependence on being, whether reality is made to consist in pure subsistent "forms" (Platonism), or in the modalities of material concreteness (Stoic and Epicurean materialism), or in the modalities of being as such (Aristotelianism).
When, however, with Kant the "thing in itself" was declared inaccessible and judgments of truth could no longer coincide with those of reality, the category was reduced to a determination of thought itself: the categories express the a priori possibility of the judgments of experience of which the physical and mathematical sciences consist (synthetic a priori judgments). Kant found twelve of them, which he divided into four groups of three each, that is, according to quantity, quality, relation and modality (Kritik der reinen Vernunft, B. 107, ed. Kehrbach 97). Seen at their root, the categories for Kant were supposed to express the forms according to which the spontaneity of the transcendental "I think" is actualized — something which, as Hegel observes, was in contradiction with their initial derivation from the traditional table of judgments: the categories must be deduced with necessity through the internal and exclusive development of the subject or of thought itself (Enc., I, §§ 42-44). Thus in the tangle of post-Kantian philosophical growth the problem of the categories lost its specific meaning and passed into second place, until it was eliminated altogether in Gentile's actualism, where the "act" is everything and all things, and always itself in everything, in the infinite process of becoming (G. Gentile, La riforma della dialettica hegeliana, 2nd ed., Messina 1923, p. 245).
In contemporary thought the notion of category tends toward ever vaguer and broader uses and is applied to indicate any classification in any order whatsoever: one speaks therefore of categories of knowing, of being, of essential, existential, logical, psychological, ethical, economic, political, religious categories, and so on; but in this way the theoretical problem that was bound up with this notion is also lost.