The Aristotelian doctrine is most distinctly formulated in the short treatise Κατηγορίαι, which generally occupies the first place among the books of the Organon. The authenticity of the treatise was doubted in early times by some of the Aristotle. commentators, and the doubts have been revived by such scholars as L. Spengel and Carl Prantl. On the other hand, C.A. Brandis, H. Bonitz, and Ed. Zeller are of opinion that the tract is substantially Aristotle’s. The matter is hardly one that can be decided either pro or con with anything like certainty; but this is of little moment, for the doctrine of the categories, even of the ten categories, does not stand or fall with only one portion of Aristotle’s works.
It is surprising that there should yet be so much uncertainty as to the real significance of the categories, and that we should be in nearly complete ignorance as to the process of thought by which, Aristotle was led to the doctrine. On both points It is difficult to extract from the matter before us anything approaching a satisfactory solution. The terms employed to denote the categories have been scrutinized with the utmost care, but they give little help. The most important—κ. τοῦ ὄντος or τῆς οὐσίας, γένη τοῦ ὄντος or τῶν ὄντων, γένη simply, τὰ πρῶτα or τὰ κοινὰ πρῶτα, αἱ πτῶσεις, or αἱ διαιρέσεις—only indicate that the categories are general classes into which Being as such may be divided, that they are summa genera. The expressions γένη τῶν κατηγορίων and σχήματα τῶν κ., which are used frequently, seem to lead to another and somewhat different view. κατηγορία being taken to mean that which is predicated, γένη τῶν κ. would signify the most general classes of predicates, the framework into the divisions of which all predicates must come. To this interpretation there are objections. The categories must be carefully distinguished from predicables; in the scholastic phraseology the former refer to first intentions, the latter to second intentions, i.e. the one denote real, the other logical connexion. Further, the categories cannot without careful explanation be defined as predicates; they are this and something more. The most important category, οὐσία, in one of its aspects cannot be predicate at all.
In the Κατηγορίαι Aristotle prefixes to his enumeration a grammatico-logical disquisition on homonyms and synonyms, and on the elements of the proposition, i.e. subject and predicate. He draws attention to the fact that things are spoken of either in the connexion known as the proposition, e.g. “a man runs,” or apart from such connexion, e.g. “man” and “runs.” He then proceeds, “Of things spoken of apart from their connexion in a proposition (τῶν κατὰ μηδεμίαν συμπλοκὴν λεγομένων), each signifies either Substance (οὐσία), or Quantity (ποσόν), or Quality (ποιόν), or Relation (πρός τι,) or Where (i.e. Place, ποῦ), or When (i.e. Time, ποτέ), or Position (κεῖσθαι), or Possession (ἔχειν), or Action (ποιεῖν), or Passion (πάσχειν). οὐσία, the first category, is subdivided into πρώτη οὐσία or primary substance, which is defined to be τόδε τι, the singular thing in which properties inhere, and to which predicates are attached, and δεύτεραι οὐσίαι, genera or species which can be predicated of primary substances, and are therefore οὐσία. only in a secondary sense. Nevertheless, they too, after a certain fashion, signify the singular thing, τόδε τι” (K. p. 3 b 12, 13). It is this doctrine of πρώτη οὐσία that has raised doubts with regard to the authenticity of the Κατηγορίαι But the tenfold classification, which has also been captiously objected to, is given in an acknowledged writing of Aristotle’s (see Topica, i. 9, p. 103 b 20).[5] At the same time it is at least remarkable that in two places where the enumeration seems intended to be complete (Met. p. 1017 a 25; An. Pos. i. 22, p. 83 a 21), only eight are mentioned, ἔχειν and κεῖσθαι being omitted. In other passages[6] six, five, four, and three are given, frequently with some addition, such as καὶ αἱ ἄλλαι κ. It is also to be observed that, despite of this wavering, distinct intimations are given by Aristotle that he regarded his list as complete, and he uses phrases which would seem to indicate that the division had been exhaustively carried out. He admits certainly that some predicates which come under one category might be referred to another, but he declines to deduce all from one highest class, or to recognize any relation of subordination among the several classes.
The full import of the categories will never be adequately reached from the point of view taken up in the Κατηγορίαι, which bears all the marks of an early and preliminary study. For true understanding we must turn to the Metaphysics, where the doctrine is handled at large. The discussion of Being in that work starts with a distinction that at once gives us a clue. τὸ ὄν is spoken of in many ways; of these four are classified—τὸ ὄν κατὰ συμβεβηκός, τὸ ὄν ὼς ὰληθές, τὸ ὄν δυνάμει καὶ ἑνεργείᾳ, and τὸ ὄν κατὰ τὰ σχήματα τῶν κατηγορίων. It is evident from this that the categories can be regarded neither as purely logical nor as purely metaphysical elements. They indicate the general forms or ways in which Being can be predicated; they are determinations of Being regarded as an object of thought, and consequently as matter of speech. It becomes apparent also why the analysis of the categories starts from the singular thing, for it is the primary form under which all that is becomes object of knowledge, and the other categories modify or qualify this real individual. Πάντα δὲ τὰ γιγνόμενα ὑπό τέ τινος γίγνεται καὶ ἔκ τινος καὶ τὶ. Τὸ δὲ τὶ λέγω καθ᾽ ἑκάστην κατηγορίαν᾽ ἢ γὰρ τόδε ἢ ποσὸν ἢ ποιὸν ἢ ποῦ (Met. p. 1032 a 13-15).... The categories, therefore, are not logical forms, but real predicates; they are the general modes in which Being may be expressed. The definite thing, that which comes forward in the process from potentiality to full actuality, can only appear and be spoken of under forms of individuality, quality, quantity and so on. The nine later categories all denote entity in a certain imperfect fashion.
The categories then are not to be regarded as heads of predicates, the framework into which predicates can be thrown. They are real determinations of Being—allgemeine Bestimmtheiten, as Hegel calls them. They are not summa genera of existences, still less are they to be explained as a classification of namable things in general. The objections Mill has taken to the list are entirely irrelevant, and would only have significance if the categories were really—what they are not—an exhaustive division of concrete existences. Grote’s view (Aristotle, i. 108) that Aristotle drew up his list by examining Various popular propositions, and throwing the different predicates into genera, “according as they stood in different logical relation to the subject,” has no foundation. The relation of the predicate category to the subject is not entirely a logical one; it is a relation of real existence, and wants the essential marks of the prepositional form. The logical relations of τὸ ὂν are provided for otherwise than by the categories.
Aristotle has given no intimation of the course of thought by which he was led to his tenfold arrangement, and it seems hopeless to discover it. Trendelenburg in various essays has worked out the idea that the root of the matter is to be found in grammatical considerations, that the categories originated from investigations into grammatical functions, and that a correspondence will be found to obtain between categories and parts of speech. Thus, Substance corresponds to noun substantive, Quantity and Quality to the adjective, Relation partly to the comparative degree and perhaps to the preposition, When and Where to the adverbs of time and place. Action to the active, Passion to the passive of the verb, Position (κεῖσθαι) to the intransitive verb, ἔχειν to the peculiar Greek perfect. That there should be a very close correspondence between the categories and grammatical elements is by no means surprising; that the one were deduced from the other is both philosophically and historically improbable. Reference to the detailed criticisms of Trendelenburg by Ritter, Bonitz, and Zeller will be sufficient.
Aristotle has also left us in doubt on another point. Why should there be only ten categories? and why should these be the ten? Kant and Hegel, it is well known, signalize as the great defect in the Aristotelian categories the want of a principle, and yet some of Aristotle’s expressions would warrant the inference that he had a principle, and that he thought his arrangement exhaustive. The leading idea of all later attempts at reduction to unity of principle, the division into substance and accident, was undoubtedly not overlooked by Aristotle, and Fr. Brentano[7] has collected with great diligence passages which indicate how the complete list might have been deduced from this primary distinction. His tabular arrangements (pp. 175, 177) are particularly deserving of attention. The results, however, are hardly beyond the reach of doubt.
There was no fundamental change in the doctrine of the categories from the time of Aristotle to that of Kant, and only two proposed reclassifications are of such importance as to require notice. The Stoics adopted a fivefold arrangement of Later Greek. highest classes, γενικώτατα. τὸ ὄν or τὶ, Being, or somewhat in general, was subdivided into ὑποκείμενα or subjects, ποιά or qualities in general, which give definiteness to the blank subject, πὼς ἔχοντα, modes which further determine the subject, and πὼς ἔχοντα, definite relative modes. These categories are so related that each involves the existence of one higher than itself, thus there cannot be a πρός τι πὼς ἔχον which does not rest upon or imply a πὼς ἔχον, but πὼς ἔχον is impossible without ποιόν, which only exists in ὑποκείμενον, a form or phase of τὸ ὄν.[8]
Plotinus, after a lengthy critique of Aristotle’s categories, sets out a twofold list. τὸ ἔν, κίνησις, στάσις, ταὐτότης, ἑτερότης are the primitive categories (πρῶτα γένη) of the intelligible sphere. οὐσία, πρός τι, ποιά, ποσόν, κίνησις are the categories of the sensible world. The return to the Platonic classification will not escape notice.
Modern philosophy, neglecting altogether the dry and tasteless treatment of the Aristotelian doctrine by scholastic writers, gave a new, a wider and deeper meaning to the categories. They now appear as ultimate or root notions, the metaphysical Modern philosophy. or thought elements, which give coherence and consistency to the material of knowledge, the necessary and universal relations which obtain among the particulars of experience. There was thus to some extent a return to Platonism, but in reality, as might easily be shown, the new interpretation was, with due allowance for difference in point of view, in strict harmony with the true doctrine of Aristotle. The modern theory dates in particular from the time of Kant, who may be said to have reintroduced the term into philosophy. Naturally there are some anticipations in earlier thinkers. The Substance, Attribute and Mode of Cartesianism can hardly be classed among the categories; nor does Leibnitz’s chance suggestion of a fivefold arrangement into Substance, Quantity, Quality, Action and Passion, and Relations, demand any particular notice. Locke, too, has a classification into Substances, Modes and Relations, but in it he has manifestly no intention of drawing up a table of categories. What in his system corresponds most nearly to the modern view of these elements is the division of kinds of real predication. In all judgments of knowledge we predicate either (1) Identity or Diversity, (2) Relation, (3) Co-existence, or necessary connexion, or (4) Real existence. From this the transition was easy to Hume’s important classification of philosophical relations into those of Resemblance, Identity, Time and Place, Quantity or Number, Quality, Contrariety, Cause and Effect.