Aristotle comments at considerable length upon the four first of the ten Categories. 1. Essence or Substance. 2. Quantity. 3. Quality. 4. Relation. As to the six last, he says little upon any of them; upon some, nothing at all. His decuple partition of _Entia_ or _Enunciata_ is founded entirely upon a logical principle. He looks at them in their relation to Propositions; and his ten classes discriminate the relation which they bear to each other as parts or constituent elements of a proposition. Aristotle takes his departure, not from any results of scientific research, but from common speech; and from the dialectic, frequent in his time, which debated about matters of common life and talk, about received and current opinions.[32] We may presume him to have studied and compared a variety of current propositions, so as to discover what were the different relations in which Subjects and Predicates did stand or could stand to each other; also the various questions which might be put respecting any given subject, with the answers suitable to be returned.[33] [Footnote 32: Waitz, ad Aristot. Categor. p. 284: "Id Categoriis non de ipsâ rerum natura et veritate exponit, sed res tales capit, quales apparent in communi vita homini philosophia non imbuto, unde fit, ut in Categoriis alia sit [Greek: prô/tê ou)si/a] et in prima philosophia: illa enim partes habet, hæc vero non componitor ex partibus." Compare Metaphys. Z. p. 1032, b. 2, and the [Greek: a)pori/a] in Z. p. 1029, a., p. 1037, a. 28. The different meaning of [Greek: prô/tê ou)si/a] in the Categoriæ and in the Metaphysica, is connected with various difficulties and seeming discrepancies in the Aristotelian theory of cognition, which I shall advert to in a future chapter. See Zeller, Philos. der Griech. ii. 2, pp. 234, 262; Heyder, Aristotelische und Hegelsche Dialektik, p. 141, seq.] [Footnote 33: Thus he frequently supposes a question put, an answer given, and the proper mode of answering. Categor. p. 2, b. 8: [Greek: e)a\n ga\r a)podidô=| tis tê\n prô/tên ou)si/an ti/ e)sti, gnôrimô/teron kai\ oi)keio/teron a)podô/sei], &c.; also ibid. p. 2, b. 32; p. 3, a. 4, 20.]