Aristotle ranks as his first and fundamental Category Substance or Essence--[Greek: Ou)si/a]; the abstract substantive word corresponding to [Greek: To\ o)/n]; which last is the vast aggregate, not generically One but only analogically One, destined to be distributed among the ten Categories as _Summa Genera_. The First _Ens_ or First Essence--that which is _Ens_ in the fullest sense--is the _individual_ concrete person or thing in nature; Sokrates, Bukephalus, this man, that horse, that oak-tree, &c. This First _Ens_ is indispensable as Subject or _Substratum_ for all the other Categories, and even for predication generally. It is a Subject only; it never appears as a predicate of anything else. As _Hic Aliquis_ or _Hoc Aliquid_, it lies at the bottom (either expressed or implied) of all the work of predication. It is _Ens_ or Essence most of all, _par excellence_; and is so absolutely indispensable, that if all First _Entia_ were supposed to be removed, neither Second _Entia_ nor any of the other Categories could exist.[34] [Footnote 34: Aristot. Categ. p. 2, a. 11, b. 6. [Greek: Ou)si/a ê( kuriô/tata kai\ prô/tôs kai\ ma/lista legome/nê--mê\ ou)sô=n ou)=n tô=n prô/tôn ou)siô=n, a)du/naton tô=n a)/llôn ti ei)=nai.]] The Species is recognized by Aristotle as a Second _Ens_ or Essence, in which these First Essences reside; it is less (has less completely the character) of Essence than the First, to which it serves as Predicate. The Genus is (strictly speaking) a Third Essence,[35] in which both the First and the Second Essence are included; it is farther removed than the Species from the First Essence, and has therefore still less of the character of Essence. It stands as predicate both to the First and to the Second Essence. While the First Essence is more Essence than the Second, and the Second more than the Third, all the varieties of the First Essence are in this respect upon an equal footing with each other. This man, this horse, that tree, &c., are all Essence, equally and alike.[36] The First Essence admits of much variety, but does not admit graduation, or degrees of more or less. [Footnote 35: Aristotle here, in the Categoriæ, ranks Genus and Species as being, both of them, [Greek: deu/terai ou)si/ai]. Yet since he admits Genus to be farther removed from [Greek: prô/tê ou)si/a] than Species is, he ought rather to have called Genus a Third Essence. In the Metaphysica he recognizes a gradation or ordination of [Greek: ou)si/a] into First, Second, and Third, founded upon a totally different principle: the Concrete, which in the Categoriæ ranks as [Greek: prô/tê ou)si/a], ranks as [Greek: tri/tê ou)si/a] in the Metaphysica. See Metaphys. [Greek: Ê]. p. 1043. a. 18-28.] [Footnote 36: Aristot. Categ. p. 2, b. 20; p. 3, b. 35.