[13] Analyt. Post. II. v. p. 91, b. 12, seq.; Analyt. Prior. I. xxxi. p. 46, a. 31. Aristotle here alludes to the method pursued by Plato in the Sophistes and Politicus, though he does not name Plato: ἡ διὰ τῶν διαιρέσεων ὁδός, &c.
[14] Analyt. Post. II. v. p. 91, b. 15-33: οὐδὲ γὰρ ὁ ἐπάγων ἴσως ἀποδείκνυσιν, ἀλλ’ ὅμως δηλοῖ τι. Compare Themistius, p. 74.
Again, neither can you arrive at the definition of a given subject, by assuming in general terms what a definition ought to be, and then declaring a given form of words to be conformable to such assumption; because your minor premiss must involve Petitio Principii. The same logical fault will be committed, if you take your departure from an hypothesis in which you postulate the definition of a certain subject, and then declare inferentially what the definition of its contrary must be. The definition which you here assume requires proof as much as that which you infer from it.[15] Moreover, neither by this process, nor by that of generic subdivision, can you show any reason why the parts of the definition should coalesce into one essential whole. If they do not thus coalesce — if they be nothing better than distinct attributes conjoined in the same subject, like musicus and grammaticus — the real essence is not declared, and the definition is not a good one.[16]
[15] Analyt. Post. II. vi. p. 92, a. 6-28. Themist. p. 76.
Rassow renders ἐξ ὑποθέσεως — “assumptâ generali definitionis notione;â€� and also says: “τὸ τί ἦν εἶναι — generalem definitionis notionem; τὸ τί ἐστιν — certam quandam definitionem, significare perspicuum est.â€� (Aristotelis de Notionis Definitione Doctrina, p. 65).
[16] Analyt. Post. II. vi. p. 92, a. 32. That the parts of the definition must coalesce into one unity is laid down again in the Metaphysica, Z. pp. 1037, 1038, where Aristotle makes reference to the Analytica as haying already treated the same subject, and professes an intention to complete what has been begun in the Analytica; ἐφ’ ὅσον ἐν τοῖς Ἀναλυτικοῖς περὶ ὁρισμοῦ μὴ εἴρηται.
After stating some other additional difficulties which seem to leave the work of Definition inexplicable, Aristotle relinquishes the dubitative treatment, and looks out for some solution of the puzzle: How may it be possible that the Definition shall become known?[17] He has already told us that to know the essence of a thing is the same as to know the cause or reason of its existence; but we must first begin by knowing that the definiendum exists; for there can be no definition of a non-entity, except a mere definition of the word, a nominal or verbal definition. Now sometimes we know the existence of the subject by one or other of its accidental attributes; but this gives us no help towards finding the definition.[18] Sometimes, however, we obtain a partial knowledge of its essence along with the knowledge of its existence; when we know it along with some constant antecedent, or through some constant, though derivative, consequent. Knowing thus much, we can often discover the cause or fundamental condition thereof, which is the essence or definition of the subject.[19] Indeed, it may happen that the constant derivative, and the fundamental essence on which it depends, become known both together; or, again, the cause or fundamental condition may perhaps not be the essence of the subject alone, but some fact including other subjects also; and this fact may then be stated as a middle term. Thus, in regard to eclipse of the moon, we know the constant phenomenal fact about it, that, on a certain recurrence of the time of full moon, the moon casts no light and makes no shadow. Hence we proceed to search out the cause. Is it interposition of the earth, or conversion of the moon’s body, or extinction of her light, &c.? The new fact when shown, must appear as a middle term, throwing into syllogistic form (in the First figure) the cause or rational explanation of a lunar eclipse; showing not merely that there is an eclipse, but what an eclipse is, or what is its definition.[20]
[17] Analyt. Post. II. vii. p. 92, a. 34, seq. The ἀπόριαι continue to the end of ch. vii. He goes on, ch. viii. p. 93, a. 1-2: πάλιν δὲ σκεπτέον τί τούτων λέγεται καλῶς, καὶ τί οὐ καλῶς, &c. “Tout ce qui précède ne représente pas la théorie proprement dite; ce n’est qu’une discussion préliminaireâ€� (Barth. St. Hilaire, not. p. 222). These difficult chapters are well illustrated by Hermann Rassow, ch. i. pp. 9-14.
[18] Analyt. Post. II. viii. p. 93, a. 3: ἐπεὶ δ’ ἐστίν, ὡς ἔφαμεν, ταὐτὸν τὸ εἰδέναι τί ἐστι καὶ τὸ εἰδέναι τὸ αἴτιον τοῦ εἰ ἔστι· Ibid. a. 24: ὅσα μὲν οὖν κατὰ συμβεβηκὸς οἴδαμεν ὅτι ἔστιν, ἀναγκαῖον μηδαμῶς ἔχειν πρὸς τὸ τί ἐστιν· οὐδὲ γὰρ ὅτι ἔστιν ἴσμεν· τὸ δὲ ζητεῖν τί ἐστι μὴ ἔχοντας ὅτι ἔστι, μηδὲν ζητεῖν ἐστίν. καθ’ ὅσων δ’ ἔχομέν τι, ῥᾷον· ὥστε ὡς ἔχομεν ὅτι ἔστιν, οὕτως ἔχομεν καὶ πρὸς τὸ τί ἐστιν. Compare Brentano, Ueber die Bedeutung des Seienden nach Aristoteles, p. 17.
[19] Analyt. Post. II. viii. p. 93, a. 21. Themistius, p. 79, Speng.: ὅσα δὲ ἀπὸ τῶν οἰκείων τε καὶ ἐξ αὐτοῦ τοῦ πράγματος, ἀπὸ τούτων ἤδη ῥᾷον εἰς τὸ τί ἐστι μεταβαίνομεν.