The different meaning of πρώτη οὐσία in the Categoriæ and in the Metaphysica, is connected with various difficulties and seeming discrepancies in the Aristotelian theory of cognition, which I shall advert to in a future chapter. See Zeller, Philos. der Griech. ii. 2, pp. 234, 262; Heyder, Aristotelische und Hegelsche Dialektik, p. 141, seq.
[33] Thus he frequently supposes a question put, an answer given, and the proper mode of answering. Categor. p. 2, b. 8: ἐὰν γὰρ ἀποδιδῷ τις τὴν πρώτην οὐσίαν τί ἐστι, γνωριμώτερον καὶ οἰκειότερον ἀποδώσει, &c.; also ibid. p. 2, b. 32; p. 3, a. 4, 20.
Aristotle ranks as his first and fundamental Category Substance or Essence — Οὐσία; the abstract substantive word corresponding to Τὸ ὄν; which last is the vast aggregate, not generically One but only analogically One, destined to be distributed among the ten Categories as Summa Genera. The First Ens or First Essence — that which is Ens in the fullest sense — is the individual concrete person or thing in nature; Sokrates, Bukephalus, this man, that horse, that oak-tree, &c. This First Ens is indispensable as Subject or Substratum for all the other Categories, and even for predication generally. It is a Subject only; it never appears as a predicate of anything else. As Hic Aliquis or Hoc Aliquid, it lies at the bottom (either expressed or implied) of all the work of predication. It is Ens or Essence most of all, par excellence; and is so absolutely indispensable, that if all First Entia were supposed to be removed, neither Second Entia nor any of the other Categories could exist.[34]
[34] Aristot. Categ. p. 2, a. 11, b. 6. Οὐσία ἡ κυριώτατα καὶ πρώτως καὶ μάλιστα λεγομένη — μὴ οὐσῶν οὖν τῶν πρώτων οὐσιῶν, ἀδύνατον τῶν ἄλλων τι εἶναι.
The Species is recognized by Aristotle as a Second Ens or Essence, in which these First Essences reside; it is less (has less completely the character) of Essence than the First, to which it serves as Predicate. The Genus is (strictly speaking) a Third Essence,[35] in which both the First and the Second Essence are included; it is farther removed than the Species from the First Essence, and has therefore still less of the character of Essence. It stands as predicate both to the First and to the Second Essence. While the First Essence is more Essence than the Second, and the Second more than the Third, all the varieties of the First Essence are in this respect upon an equal footing with each other. This man, this horse, that tree, &c., are all Essence, equally and alike.[36] The First Essence admits of much variety, but does not admit graduation, or degrees of more or less.
[35] Aristotle here, in the Categoriæ, ranks Genus and Species as being, both of them, δεύτεραι οὐσίαι. Yet since he admits Genus to be farther removed from πρώτη οὐσία than Species is, he ought rather to have called Genus a Third Essence. In the Metaphysica he recognizes a gradation or ordination of οὐσία into First, Second, and Third, founded upon a totally different principle: the Concrete, which in the Categoriæ ranks as πρώτη οὐσία, ranks as τρίτη οὐσία in the Metaphysica. See Metaphys. Η. p. 1043, a. 18-28.
[36] Aristot. Categ. p. 2, b. 20; p. 3, b. 35.
Nothing else except Genera and Species can be called Second Essences, or said to belong to the Category Essence; for they alone declare what the First Essence is. If you are asked respecting Sokrates, What he is? and if you answer by stating the Species or the Genus to which he belongs — that he is a man or an animal — your answer will be appropriate to the question; and it will be more fully understood if you state the Species than if you state the Genus. But if you answer by stating what belongs to any of the other Categories (viz., that he is white, that he is running), your answer will be inappropriate, and foreign to the question; it will not declare what Sokrates is.[37] Accordingly, none of these other Categories can be called Essences. All of them rank as predicates both of First and of Second Essence; just as Second Essences rank as predicates of First Essences.[38]
[37] Ibid. p. 2, b. 29-37. εἰκότως δὲ μετὰ τὰς πρώτας οὐσίας μόνα τῶν ἄλλων τὰ εἴδη καὶ τὰ γένη δεύτεραι οὐσίαι λέγονται· μόνα γὰρ δηλοῖ τὴν πρώτην οὐσίαν τῶν κατηγορουμένων. τὸν γάρ τινα ἄνθρωπον ἐὰν ἀποδιδῷ τις τί ἐστι, τὸ μὲν εἶδος ἢ τὸ γένος ἀποδιδοὺς οἰκείως ἀποδώσει, καὶ γνωριμώτερον ποιήσει ἄνθρωπον ἢ ζῷον ἀποδιδούς· τῶν δὲ ἄλλων ὅ, τι ἂν ἀποδιδῷ τις, ἀλλοτρίως ἔσται ἀποδεδωκώς, οἷον λευκόν ἢ τρέχει ἢ ὁτιοῦν τῶν τοιούτων ἀποδιδούς. Ὥστε εἰκότως τῶν ἄλλων ταῦτα μόνα οὐσίαι λέγονται.
[38] Ibid. p. 3, a. 2.