[Greek: Ta\ a)/ra lego/mena e)pi\ tô=n a(plô=s e)pistêtô=n kath' au(ta\ ou(/tôs ô(s e)nupa/rchein toi=s katêgoroume/nois ê)\ e)nupa/rchesthai di' au(ta/ te/ e)sti kai\ e)x a)na/gkês] (b. 16, seq.). _Line_ must be included in the definition of the opposites _straight_ or _curve_. Also it is essential to every line that it is either straight or curve. _Number_ must be included in the definition of the opposites _odd_ or _even_; and to be either odd or even is essentially predicable of every number. You cannot understand what is meant by _straight_ or _curve_ unless you have the notion of a _line_. The example given by Aristotle of _causal_ conjunction (the death of an animal under the sacrificial knife) shows that he had in his mind the perfection of Inductive Observation, including full application of the Method of Difference.] [Footnote 17: Aristot. Analyt. Post. I. iv. p. 73, b. 25-p. 74, a. 3. [Greek: o(\ toi/nun _to\ tucho\n prô=ton_ dei/knutai du/o o)rtha\s e)/chon ê)\ o(tiou=n a)/llo, tou/tô| prô/tô| u(pa/rchei katho/lou, kai\ ê( _a)po/deixis kath' au(to\_ tou/tou katho/lou e)sti\, tô=n d' a)/llôn tro/pon tina\ ou) kath' au(to/; ou)de\ tou= i)soske/lous ou)k e)/sti katho/lou a)ll' e)pi\ ple/on.] About the precise signification of [Greek: katho/lou] in Aristotle, see a valuable note of Bonitz (ad Metaphys. Z. iii.) p. 299; also Waitz (ad Aristot. De Interpr. c. vii.) I. p. 334. Aristotle gives it here, b. 26: [Greek: katho/lou de\ le/gô o(\ a)\n kata\ panto/s te u(pa/rchê| kai\ kath' au(to\ kai\ ê(=| au)to/.] Compare Themistius, Paraphr. p. 19, Spengel. [Greek: To\ kath' au(to/] is described by Aristotle confusedly. [Greek: To\ katho/lou], is that which is predicable of the subject as a whole or _summum genus_: [Greek: to\ kata\ panto/s], that which is predicable of every individual, either of the _summum genus_ or of any inferior species contained therein. Cf. Analyt. Post. I. xxiv. p. 85, b. 24: [Greek: ô(=| ga\r kath' au(to\ u(pa/rchei ti, tou=to au)to\ au(tô=| ai)/tion]--the subject is itself the cause or _fundamentum_ of the properties _per se_. See the explanation and references in Kampe, Die Erkenntniss-theorie des Aristoteles, ch. v. pp. 160-165.]