Note 16 — Chapter VII · ANALYTICA POSTERIORA I.

Aristot. Analyt. Post. I. iv. p. 73, a. 21, b. 16.

Τὰ ἄρα λεγόμενα ἐπὶ τῶν ἁπλῶς ἐπιστητῶν καθ’ αὑτὰ οὕτως ὡς ἐνυπάρχειν τοῖς κατηγορουμένοις ἢ ἐνυπάρχεσθαι δι’ αὑτά τέ ἐστι καὶ ἐξ ἀνάγκης (b. 16, seq.). Line must be included in the definition of the opposites straight or curve. Also it is essential to every line that it is either straight or curve. Number must be included in the definition of the opposites odd or even; and to be either odd or even is essentially predicable of every number. You cannot understand what is meant by straight or curve unless you have the notion of a line.

The example given by Aristotle of causal conjunction (the death of an animal under the sacrificial knife) shows that he had in his mind the perfection of Inductive Observation, including full application of the Method of Difference.