68 Dr. WHEWELL'S CRITICISM OF ARISTOTLE S ACCOUNT OF INDUCTION. 



as horned, as hoofed, and the contrary; but not as acholous and the contrary. When he looked 

 at animals in that point of view, — when he took up that character as the ground of distinction, 

 he forthwith imagined that he found a separation of long-lived and short-lived animals. 

 When that Fact became a Conception, he obtained an inductive truth, or, at any rate, an 

 inductive proposition. 



He obtained an inductive proposition by applying the Conception acholous to his obser- 

 vation of animals. This Conception divided them into two classes; and these classes were, 

 he fancied, long-lived and short-lived respectively. That it was the Conception, and not the 

 Fact which enabled him to obtain his inductive proposition, is further plain from this, that 

 the supposed Fact is not a fact. Acholous animals are not longer-lived than others. The 

 presence or absence of the gall-bladder is no character of longevity. It is true, that in one 

 familiar class of animals, the herbivorous kind, there is a sort of first seeming of the truth 

 of Aristotle's asserted rule : for the horse and mule which have not the gall-bladder are 

 longer-lived than the cow, sheep, and goat, which have it. But if we pursue the investigation 

 further, the rule soon fails. The deer-tribe that want the gall-bladder are not longer-lived 

 than the other ruminating animals which have it. And as a conspicuous evidence of the 

 falsity of the rule, man and the elephant are perhaps, for their size, the longest-lived animals, 

 and of these, man has, and the elephant has not, the organ in question. The inductive 

 proposition, then, is false ; but what we have mainly to consider is, where the fallacy enters, 

 according to Aristotle's analysis of Induction into Syllogism. For the two premisses are still 

 true; that elephants, &c, are long-lived; and that elephants, &c, are acholous. And it 

 is plain that the fallacy comes in with that conversion and generalization of the latter propo- 

 sition, which we have noted as necessary to Aristotle's illustration of Induction. When we 

 say " All acholous animals are as elephants, &c," that is, as those in their biological con- 

 ditions, we say what is not true. Aristotle's condition (§ 8), is not complied with, that the 

 middle term shall not extend beyond the extreme. For the character acholous does extend 

 beyond the elephant and the animals biologically resembling it ; it extends to deer, &c., which 

 are not like elephants and horses, in the point in question. And thus, we see that the 

 assumed conversion and generalization of the minor proposition, is the seat of the fallacy of 

 false Inductions, as it is the seat of the peculiar logical character of true inductions. 



As true Inductive Propositions cannot be logically demonstrated by syllogistic rules, so 

 they cannot be discovered by any rule. There is no formula for the discovery of inductive 

 truth. It is caught by a peculiar sagacity, or power of divination, for which no precepts 

 can be given. But from what has been said, we see that this sagacity shews itself in the 

 discovery of propositions which are both true, and convertible in the sense above explained. 

 Both these steps may be difficult. The former is often very laborious : and when the labour 

 has been expended, and a true proposition obtained, it may turn out useless, because the 

 proposition is not convertible. It was a matter of great labour to Kepler to prove (from 

 calculation of observations) that Mars moves elliptically. Before he proved this, he had tried 

 to prove many similar propositions: — that Mars moved according to the "bisection of the 

 eccentricity,'' — according to the " vicarious hypothesis," — according to the "physical hypo- 

 thesis," — and the like ; but none of these was found to be exactly true. The proposition 



