[267] Ibid. a. 20. This last condition is a high measure of perfection to exact from a definition. Assuredly Aristotle’s own definitions often fall lamentably short of it.
Such are the Loci regarding Indistinctness in the setting out of the definition. The second defect is Redundancy.
1. Redundancy will arise if the terms of the definition include either all things absolutely, or all things contained in the same genus as the definiend; since the definition ought to consist of a generic term to discriminate the definiend from all extra-generic things, and a differential term to discriminate it from other things within the same genus. A definition of the kind mentioned will be useless through redundancy.[268] It will also be open to the like objection, if it includes what is merely a proprium of the definiend, over and above the essential attributes; or, indeed, if it includes any thing else except what is required for clearly bringing out the definiend.[269] It will be still worse, if it comprises any attribute not belonging to all individuals of the species; for then it will not even be a proprium or a reciprocating predication.[270]
[268] Topic. VI. iii. p. 140, a. 23-32. Alexander, however, remarks very pertinently, that the defects of such a definition are defects of substance rather than of expression. Aristotle has passed unconsciously from the latter to the former: ἐν μὲν τῇ πρώτῃ τῶν ἐφόδων δόξειεν ἂν ὁ Ἀριστοτέλης μετάγειν εἰς τὰς πραγματικὰς ἐξετάσεις (Schol. p. 287, b. 27, Br.).
[269] Ibid. a. 37: ἁπλῶς δ’ εἰπεῖν, ἅπαν περίεργον οὗ ἀφαιρεθέντος τὸ λοιπὸν δῆλον ποιεῖ τὸ ὁριζόμενον.
[270] Ibid. b. 16.
2. Repetition is another fault sometimes committed. The same attribute may be predicated twice over. Or a particular and narrow attribute may be subjoined, in addition to a more general and comprehensive attribute in which it has already been included.[271]
[271] Ibid. b. 27-p. 141, a. 22.
So much for the faults which belong to the manner of expressing the definition tendered. Next, as bearing on the matter and substance of the definition, the following loci are distinguishable.
1. The first of these loci is, if the matter of the definition is not prius and notius as compared with the definiend. It is one of the canons of Definition, the purpose of which is to impart knowledge of the definiend, to introduce nothing except what is prior by nature and better known than the latter. The essence of each definiend — the being what it is — is one and only one. If a definition be given, other than that by means of what is prius and notius, it would follow that the same definiend might have two distinct essences; which is impossible. Accordingly, any proposition tendered as a definition but enunciating what is not prior by nature and better known than the definiend sins against this canon, and is to be held as no true definition at all.[272]