[Footnote 57: Analyt. Post. II. xvi. p. 98, a. 35, seq. Themistius, pp. 96-97: [Greek: ou) ga/r e)stin ai)/tion tou= tê\n gê=n e)n me/sô| ei)=nai to\ tê\n selê/nên e)klei/pein, a)lla\ me/son tou= sullogismou=; kai\ tou= sumpera/smatos i)/sôs ai)/tion, _tou= pra/gmatos de\ ou)damô=s_.] Themistius here speaks with a precision which is not always present to the mind of Aristotle; for he discriminates the cause of _the fact_ from the cause of the _affirmed fact_ or _conclusion_. M. Barthélemy St. Hilaire says (Plan Général des Derniers Analytiques, p. cxl.):--"Ainsi, la démonstration de l'effet par la cause apprend pourquoi la chose est; la démonstration par l'effet apprend seulement que la chose est. On sait que la terre s'interpose, mais on ne sait pas pourquoi elle s'interpose: et ce qui le montre bien, c'est que l'idée de l'interposition de la terre est indispensable à la définition essentielle de l'éclipse tandis que l'idée de l'éclipse n'a que faire dans la définition de l'interposition. L'interposition de la terre fait donc comprendre l'éclipse; tandis que l'éclipse ne fait pas du tout comprendre l'interposition de la terre."] The question then arises, Can there be more than one cause of the same _causatum_? Is it necessary that the same effect should be produced in all cases by the same cause? In other words, when the same predicate is demonstrated to be true of two distinct minors, may it not be demonstrated in one case by one middle term, and in the other case by a different middle term?[58] Answer: In genuine and proper scientific problems the middle term is the rational account (definition, interpretation) of the major extreme; this middle term therefore, or the cause, must in all cases be one and the same. The demonstration in these cases is derived from the same essence; it is _per se_, not _per accidens_. But there are other problems, not strictly and properly scientific, in which cause and _causatum_ are connected merely _per accidens_; the demonstration being operated by a middle term which is not of the essence of the major, but is only a sign or concomitant.[59] According as the terms of the conclusion are related to each other, so also will the middle term be related to both. If the conclusion be equivocal, the middle term will be equivocal also; if the predicate in the conclusion be in generic relation to the subject, the major also will be in generic relation to the middle. Thus, if you are demonstrating that one triangle is similar to another, and that one colour is similar to another, the word similar in these two cases is not univocal, but equivocal; accordingly, the middle term in the demonstration will also be equivocal. Again, if you are demonstrating that four proportionals will also be proportionals alternately, there will be one cause or middle term, if the subject of the conclusion be lines; another, if the subject be numbers. Yet the middle term or cause in both is the