[38] Ibid. viii. p. 103, b. 3: μία μὲν πίστις ἡ διὰ τῆς ἐπαγωγῆς· εἰ γάρ τις ἐπισκοποίη ἑκάστην τῶν προτάσεων καὶ τῶν προβλημάτων, φαίνοιτ’ ἂν ἢ ἀπὸ τοῦ ὅρου ἢ &c.
[39] Topic. I. viii. p. 103, b. 6-19: ἄλλη δὲ πίστις ἡ διὰ συλλογισμοῦ.
It will be observed that Aristotle here resolves Definition into Genus and Differentiæ — ἐπειδὴ ὁ ὁρισμὸς ἐκ γένους καὶ διαφορῶν ἐστίν. Moreover, though he does not recognize Species as a separate head, yet in his definition of Genus he implies Species as known — γένος ἐστὶ τὸ κατὰ πλειόνων καὶ διαφερόντων τῷ εἴδει ἐν τῷ τί ἐστι κατηγορούμενον (p. 102, a. 31).
It thus appears that the quintuple classification is the real and logical one; but the quadruple may perhaps be more suitable for the Topica, with a view to dialectic procedure, since debates turn upon the attack and defence of a Definition.
Moreover, each of the four Predicables must fall under one or other of the ten Categories or Predicaments. If the predicate be either of Genus or Definition, declaring the essence of the subject, it may fall under any one of the ten Categories; if of Proprium or Accident, not declaring essence, it cannot belong to the first Category (Οὐσία), but must fall under one of the remaining nine.[40]
[40] Ibid. ix. p. 103, b. 20-39.
The notion of Sameness or Identity occurs so often in dialectic debate, that Aristotle discriminates its three distinct senses or grades: (1) Numero; (2) Specie; (3) Genere. Water from the same spring is only idem specie, though the resemblance between two cups of water from the same spring is far greater than that between water from different sources. Even Idem Numero has different significations: sometimes there are complete synonyms; sometimes an individual is called by its proprium, sometimes by its peculiar temporary accident.[41]
[41] Ibid. vii. p. 103, a. 6-39.
Having thus classified dialectic propositions, Aristotle proceeds to the combination of propositions, or dialectic discourse and argument. This is of two sorts, either Induction or Syllogism; of both which we have already heard in the Analytica. Induction is declared to be plainer, more persuasive, nearer to sensible experience, and more suitable to the many, than Syllogism; while this latter carries greater compulsion and is more irresistible against professed disputants.[42] A particular example is given to illustrate what Induction is. But we remark that though it is always mentioned as an argumentative procedure important and indispensable, yet neither here nor elsewhere does Aristotle go into any discriminative analysis of the conditions under which it is valid, as he does about Syllogism in the Analytica Priora.
[42] Ibid. xii. p. 105, a. 10-19: πόσα τῶν λόγων εἴδη τῶν διαλεκτικῶν, &c.