[Footnote 25: The difference of opinion as to the proper mode of describing the Differentia--whether by the concrete word [Greek: pezo\n], or by the abstract [Greek: pezo/tês]--gives occasion to an objection against Aristotle's view, and to a reply from Dexippus not very conclusive (Dexippus, book ii. s. 22, pp. 60, 61, ed. Spengel).] [Footnote 26: Categor. p. 3, a. 3. In the Physica, iv. p. 210, a. 14-30, Aristotle enumerates nine different senses of the phrase [Greek: e(/n tini]. His own use of the phrase is not always uniform or consistent. If we compare the Scholia on the Categoriæ, pp. 44, 45, 53, 58, 59, Br., with the Scholia on the Physica, pp. 372, 373, Br., we shall see that the Commentators were somewhat embarrassed by his fluctuation. The doctrine of the Categoriæ was found especially difficult in its application to the Differentia. In Analyt. Post. i. p. 83, a. 30, Aristotle says, [Greek: o(/sa de\ mê\ ou)si/an sêmai/nei, dei= kata/ tinos u(pokeime/nou katêgorei=sthai], which is at variance with the language of the Categoriæ, as the Scholiast remarks, p. 228, a. 33. The like may be said about Metaphys. B. p. 1001, b. 29; [Greek: D]. p. 1017, b. 13. See the Scholia of Alexander, p. 701, b. 25, Br. See also De Gener. et Corrupt. p. 319, b. 8; Physic. i. p. 185, a. 31: [Greek: ou)the\n ga\r tô=n a)/llôn chôristo/n e)sti para\ tê\n ou)si/an; pa/nta ga\r kath' u(pokeime/nou tê=s ou)si/as le/getai], where Simplikius remarks that the phrase is used [Greek: a)nti\ tou= e)n u(pokeime/nô|] (Schol. p. 328, b. 43).] Lastly, Aristotle here makes one important observation respecting those predicates which he describes as (not _in a Subject_ but) _affirmed_ or _denied of_ a Subject--_i.e._ the essential predicates. In these (he says) whatever predicate can be truly affirmed or denied of the predicate, the same can be truly affirmed or denied of the Subject.[27] This observation deserves notice, because it is in fact a brief but distinct announcement of his main theory of the Syllogism; which theory he afterwards expands in the Analytica Priora, and traces into its varieties and ramifications. [Footnote 27: Categor. p. 1, b. 10-15.]