[222] Ibid. b. 8-18.
3. Again, the respondent may perhaps affirm the subject itself as a proprium of something inherent in the subject. You may refute this by showing that, if it were so, the same thing would be a proprium of several things differing from each other in species. On the other hand, the respondent may perhaps deny that something inherent in the subject is a proprium: you may then refute him by showing that it is truly predicable of the subject only, and not truly predicable of any thing else.[223]
[223] Ibid. b. 19-34. Alexander, in the Scholia (p. 285, a. 14, Br.) has stated this locus more clearly than Aristotle — τὸ γὰρ ἴδιον ὑπάρχειν δεῖ ἐν ἑτέρῳ, οὐχ ἕτερον ἐν αὐτῷ.
4. The respondent may perhaps affirm as a proprium something contained in the essence of the subject: if so, you will refute him by showing this. On the other hand, if he denies something to be a proprium, you will refute him by showing that, though it is not contained in the essence of the subject, it is nevertheless predicable co-extensively therewith.[224]
[224] Topic. V. iv. p. 132, b. 35-p. 133, a. 11.
5. The respondent may affirm as a proprium that which is not a necessary concomitant of the subject, but may either precede or follow it. Or, on the other hand, he may deny something to be a proprium which you can show to be a constant and necessary concomitant of the subject, without being included either in its definition or differentia. In each case you will have a ground for refuting him.[225]
[225] Topic. V. iv. p. 133, a. 12-23.
6. The respondent may affirm as a proprium of the subject what he has already denied of the same subject under some other name; or he may deny of it what he has already affirmed of it under some other name. You will have grounds for refuting him.[226]
[226] Ibid. a. 24-32.
7. If there be two subjects (e.g., man and horse) the same with each other in species, the respondent may affirm respecting one of them a proprium which is not the same in species with the proprium of the other. Thus, it is not a constant proprium of horse to stand still spontaneously; accordingly neither is it a constant proprium of man to move spontaneously; these two propria being the same in species, and belonging both to man and to horse quatenus animal.[227] If, therefore, the respondent affirms the one while he denies the other, you have an argument in refutation. On the other hand, he may propound as thesis the denial of the one proprium, while he affirms or admits the other. Here too you will be able to make good the counter-affirmation against his denial, on the ground of that which he admits. Thus, if it be proprium of man to be a walking-biped, it must also be proprium of bird to be a flying-biped. The two pairs, man and bird, walking and flying, are the same in species with each other, since both pairs are subordinates under the same genus: man and bird are species, flying and walking are differentiæ, under the same genus animal. This locus, however, is not universally applicable; for perhaps one of the two predicates may not be of exclusive application to the subject, but may belong to other subjects also. Thus walking-biped designates only one variety — man; but walking-quadruped designates several — horse, ass, dog, &c. Walking-quadruped therefore is not a proprium of horse.[228]