442 INDUCTION. 



properties are said to have been found disjoined from others which have 

 always been known to accompany them ; as in the case of Pliny's men, or 

 any other kind of animal of a structure different from that which has al- 

 ways been found to co-exist with animal life. On the mode of dealing with 

 any such case, little needs be added to what has been said on the same top- 

 ic in the twenty-second chapter.* When the uniformities of co-existence 

 which the alleged fact would violate, are such as to raise a strong presump- 

 tion of their being the result of causation, the fact which conflicts vvitli 

 them is to be disbelieved; at least provisionally, and subject to further in- 

 vestigation. When the presumption amounts to a virtual certainty, as in 

 the case of the general structure of organized beings, the only question re- 

 quiring consideration is whether, in phenomena so little understood, there 

 may not be liabilities to counteraction from causes hitherto unknown ; or 

 whether the phenomena may not be capable of originating in some other 

 way, which would produce a different set of derivative uniformities. Where 

 (as in the case of the flying fish, or the ornithorhynchus) the generalization 

 to which the alleged fact would be an exception is very special and of lim- 

 ited range, neither of the above suppositions can be deemed very improba- 

 ble ; and it is generally, in the case of such alleged anomalies, wise to sus- 

 pend our judgment, pending the subsequent inquiries which will not fail 

 to confirm the assertion if it be true. But when the generalization is very 

 comprehensive, embracing a vast number and variety of observations, and 

 covering a considei'able province of the domain of nature ; then, for reasons 

 which have been fully explained, such an empirical law comes near to the 

 certainty of an ascertained law of causation ; and any alleged exception to 

 it can not be admitted, unless on the evidence of some law of causation 

 proved by a still more complete induction. 



Such uniformities in the course of nature as do not bear marks of be- 

 ing the results of causation are, as we have already seen, admissible as 

 universal truths with a degree of credence proportioned to their general- 

 ity. Those which are true of all things whatever, or at least which are 

 totally independent of the varieties of Kinds, namely, the laws of number 

 and extension, to which we may add the law of causation itself, are proba- 

 bly the only ones, an exception to which is absolutely and permanently in- 

 credible. Accordingly, it is to assertions supposed to be contradictory to 

 these laws, or to some others coming near to them in generality, that the 

 word impossibility (at least total impossibility) seems to be generally con- 

 fined. Violations of other laws, of special laws of causation, for instance, 

 are said, by persons studious of accuracy in expression, to be impossible 

 in the circumstances of the case ; or impossible unless some cause had ex- 

 isted which did not exist in the particular case.f Of no assertion, not in 



* Supra, p. 413. 



t A writer to whom I have several times referred, gives as the definition of an impossibility, 

 that which there exists in the world no cause adequate to produce. This definition does not 

 take in such impossibilities as these — that two and two should make five ; that two straight 

 lines should inclose a space ; or that any thing should begin to exist without a cause. I can 

 think of no definition of impossibility compi-ehensive enough to include all its varieties, ex- 

 cept the one which I have given : viz.. An impossibility is that, the truth of which would con- 

 flict with a complete induction, that is, with the most conclusive evidence which we possess 

 of universal truth. 



As to the reputed impossibilities which rest on no other grounds than our ignorance of any 

 cause capable of producing the supposed effects ; very few of them are certainly impossible, or 

 permanently incredible. The facts of traveling seventy miles an iiour, painless sui-gical oper- 

 ations, and conversing by instantaneous signals between London and New York, held a high 

 place, not many years ago, among such impossibilities. 



