[Footnote 49: Ibid. p. 43, a. 39: [Greek: plê\n ei) mê\ kata\ do/xan]. Cf. Schol. of Alexander, p. 175, a. 44, Br.: [Greek: e)ndo/xôs kai\ dialektikô=s, ô(/sper ei)=pen e)n toi=s Topikoi=s], that even the _principia_ of science may be debated; for example, in book B. of the Metaphysica. Aristotle does not recognize either [Greek: to\ o)/n] or [Greek: to\ e(/n] as true genera, but only as predicates.] [Footnote 50: Ibid. a. 40-43.] You must begin by putting down, along with the matter in hand itself, its definition and its _propria_; after that, its other predicates; next, those predicates which _cannot_ belong to it; lastly, those other subjects, of which it may itself be predicated. You must classify its various predicates distinguishing the essential, the _propria_, and the accidental; also distinguishing the true and unquestionable, from the problematical and hypothetical.[51] You must look out for those predicates which belong to it as subject universally, and not to certain portions of it only; since universal propositions are indispensable in syllogistic proof, and indefinite propositions can only be reckoned as particular. When a subject is included in some larger genus--as, for example, man in animal--you must not look for the affirmative or negative predicates which belong to animal universally (since all these will of course belong to man also) but for those which distinguish man from other animals; nor must you, in searching for those lower subjects of which man is the predicate, fix your attention on the higher genus animal; for animal will of course be predicable of all those of which man is predicable. You must collect what pertains to man specially, either as predicate or subject; nor merely that which pertains to him necessarily and universally, but also usually and in the majority of cases; for most of the problems debated belong to this latter class, and the worth of the conclusion will be co-ordinate with that of the premisses.[52]** Do not select predicates that are predicable[53] both of the predicate and subject; for no valid affirmative conclusion can be obtained from them. [Footnote 51: Analyt. Prior. I. xxvii. p. 43, b. 8: [Greek: kai\ tou/tôn poi=a doxastikô=s kai\ poi=a kat' a)lê/theian.]] [Footnote 52: Ibid. I. xxvii. p. 43, b. 10-35.]