Respecting the logical distinction, which Aristotle places in the commencement of this treatise on the Categories — between predicates which are affirmed of a Subject, and predicates which are in a Subject[23] — we may remark that it turns altogether upon the name by which you describe the predicate. Thus he tells us that the Species and Genus (man, animal), and the Differentia (rational), may be predicated of Sokrates, but are not in Sokrates; while knowledge is in Sokrates, but cannot be predicated of Sokrates; and may be predicated of grammar, but is not in grammar. But if we look at this comparison, we shall see that in the last-mentioned example, the predicate is described by an abstract word (knowledge); while in the preceding examples it is described by a concrete word (man, animal, rational).[24] If, in place of these three last words, we substitute the abstract words corresponding to them — humanity, animality, rationality — we shall have to say that these are in Sokrates, though they cannot (in their abstract form) be predicated of Sokrates, but only in the form of their concrete paronyms, which Aristotle treats as a distinct predication. So if, instead of the abstract word knowledge, we employ the concrete word knowing or wise, we can no longer say that this is in Sokrates, and that it may be predicated of grammar. Abstract alone can be predicated of abstract; concrete alone can be predicated of concrete; if we describe the relation between Abstract and Concrete, we must say, The Abstract is in the Concrete — the Concrete contains or embodies the Abstract. Indeed we find Aristotle referring the same predicate, when described by the abstract name, to one Category; and when described by the concrete paronymous adjective, to another and different Category.[25] The names Concrete and Abstract were not in the philosophical vocabulary of his day. In this passage of the Categoriæ, he establishes a distinction between predicates essential and predicates non-essential; the latter he here declares to be in the Subject, the former not to be in it, but to be co-efficients of its essence. But we shall find that he does not adhere to this distinction even throughout the present treatise, still less in other works. It seems to be a point of difference between the Categoriæ on one side, and the Physica and Metaphysica on the other, that in the Categoriæ he is more disposed to found supposed real distinctions on verbal etiquette, and on precise adherence to the syntactical structure of a proposition.[26]
[23] The distinction is expressed by Ammonius (Schol. p. 51, b. 46) as follows:— αἱ πρῶται οὐσίαι ὑποκεῦνται πᾶσιν, ἀλλ’ οὐχ ὁμοίως· τοῖς μὲν γὰρ πρὸς ὕπαρξιν, τούτεστι τοῖς συμβεβηκόσιν, τοῖς δὲ πρὸς κατηγορίαν, τούτεστι ταῖς καθόλου οὐσίαις.
[24] Ueberweg makes a remark similar to this. — System der Logik, sect. 56, note, p. 110, ed. second.
[25] The difference of opinion as to the proper mode of describing the Differentia — whether by the concrete word πεζὸν, or by the abstract πεζότης — gives occasion to an objection against Aristotle’s view, and to a reply from Dexippus not very conclusive (Dexippus, book ii. s. 22, pp. 60, 61, ed. Spengel).
[26] Categor. p. 3, a. 3. In the Physica, iv. p. 210, a. 14-30, Aristotle enumerates nine different senses of the phrase ἕν τινι. His own use of the phrase is not always uniform or consistent. If we compare the Scholia on the Categoriæ, pp. 44, 45, 53, 58, 59, Br., with the Scholia on the Physica, pp. 372, 373, Br., we shall see that the Commentators were somewhat embarrassed by his fluctuation. The doctrine of the Categoriæ was found especially difficult in its application to the Differentia.
In Analyt. Post. i. p. 83, a. 30, Aristotle says, ὅσα δὲ μὴ οὐσίαν σημαίνει, δεῖ κατά τινος ὑποκειμένου κατηγορεῖσθαι, which is at variance with the language of the Categoriæ, as the Scholiast remarks, p. 228, a. 33. The like may be said about Metaphys. B. p. 1001, b. 29; Δ. p. 1017, b. 13. See the Scholia of Alexander, p. 701, b. 25, Br.
See also De Gener. et Corrupt. p. 319, b. 8; Physic. i. p. 185, a. 31: οὐθὲν γὰρ τῶν ἄλλων χωριστόν ἐστι παρὰ τὴν οὐσίαν· πάντα γὰρ καθ’ ὑποκειμένου τῆς οὐσίας λέγεται, where Simplikius remarks that the phrase is used ἀντὶ τοῦ ἐν ὑποκειμένῳ (Schol. p. 328, b. 43).
Lastly, Aristotle here makes one important observation respecting those predicates which he describes as (not in a Subject but) affirmed or denied of a Subject — i.e. the essential predicates. In these (he says) whatever predicate can be truly affirmed or denied of the predicate, the same can be truly affirmed or denied of the Subject.[27] This observation deserves notice, because it is in fact a brief but distinct announcement of his main theory of the Syllogism; which theory he afterwards expands in the Analytica Priora, and traces into its varieties and ramifications.
[27] Categor. p. 1, b. 10-15.
After such preliminaries, Aristotle proceeds[28] to give the enumeration of his Ten Categories or Predicaments; under one or other of which, every subject or predicate, considered as capable of entering into a proposition, must belong: 1. Essence or Substance; such as, man, horse. 2. How much or Quantity; such as, two cubits long, three cubits long. 3. What manner of or Quality; such as, white, erudite. 4. Ad aliquid — To something or Relation; such as, double, half, greater. 5. Where; such as, in the market-place, in the Lykeium. 6. When; such as, yesterday, last year. 7. In what posture; such as, he stands up, he is sitting down. 8. To have; such as, to be shod, to be armed. 9. Activity; such as, he is cutting, he is turning. 10. Passivity; such as, he is being cut, he is being burned.