Under these canons of dialectic debate, each question was required to be really and truly one, so as to admit of a definite answer in one word. The questioner was either unfair or unskilful, if he wrapped up two questions really distinct in the same word, and thus compelled the respondent either to admit them both, or to deny them both, at once. Against this inconvenience Aristotle seeks to guard, by explaining what are the conditions under which one and the same word does in fact include more than one question. He had before brought to view the case of an equivocal term, which involves such duplication: if _himation_ means both horse and man, it will often happen that questions respecting _himation_ cannot be truly answered either by Yes or No. He now brings to view a different case in which the like ambiguity is involved. To constitute one proposition, it is essential both that the subject should be one, and that the predicate should be one; either of them indeed may be called by two or three names, but these names must coalesce into one. Thus, _animal_, _bipes_, _mansuetum_, coalesce into _homo_, and may be employed either as one subject or as one predicate; but _homo_, _albus_, _ambulans_, do not coalesce into one; so that if we say, _Kallias est homo, albus, ambulans_, the proposition is not one but three.[34] Accordingly, the respondent cannot make one answer to a question thus complicated. We thus find Aristotle laying down principles--and probably no one had ever attempted to do so before him--for the correct management of that dialectical debate which he analyses so copiously in the Topica. [Footnote 34: Aristot. De Interpret. p. 20, b. 2. seq.; Ammonius, Schol. pp. 127-128, a. 21, Br. Compare De Sophist. Elench. p. 169, a. 6-15.] There are cases (he proceeds to state) in which two predicates may be truly affirmed, taken separately, respecting a given subject, but in which they cannot be truly affirmed, taken together.[35] Kallias is a _currier_, Kallias is _good_--both these propositions may be true; yet the proposition, Kallias is a _good currier_, may not be true. The two predicates are both of them accidental co-inhering in the same individual; but do not fuse themselves into one. So, too, we may truly say, Homer _is a poet_; but we cannot truly say, Homer _is_.[36] We see by this last remark,[37] how distinctly Aristotle assigned a double meaning to _est_: first, _per se_, as meaning existence; next, relatively, as performing the function of copula in predication. He tells us, in reply either to Plato or to some other contemporaries, that though we may truly say, _Non-Ens est opinabile_, we cannot truly say _Non-Ens est_, because the real meaning of the first of these propositions is, **_Non-Ens est opinabile non esse_.[38] [Footnote 35: Aristot. De Interpr. p. 21, a. 7, seq.] [Footnote 36: Ibid. a. 27.] [Footnote 37: Compare Schol. (ad Anal. Prior. I.) p. 146, a. 19-27; also Eudemi Fragment. cxiv. p. 167, ed. Spengel.