136 THE SCIENCE OF LOGIC 



sible in varied circumstances, and by seeing whether this tallies 

 with what we should expect, that we can hope to verify our hy 

 pothesis. The only means we have of going beyond the general 

 assertion we can make in virtue of the principle of causality that 

 the phenomenon (C) has a determining cause the only means of 

 discovering the latter, of detecting its whereabouts, and bringing it 

 to light, is by supposing it to be some definite cause of a certain 

 kind (say X], and then trying to verify this supposition by the 

 employment of some processes that may lead with certainty to X 

 as the only possible cause of the phenomenon in question, the only 

 possible element, amongst all the surroundings of the pheno 

 menon, which can be the determining cause of the latter. When 

 we have discovered that the supposed cause, X, is the only possible 

 cause of the phenomenon, then, and then only, can we infer, from 

 the reality of C, that the supposed cause, X, is its real cause ; for 

 X is an antecedent of which C is the consequent, and from the 

 reality of C we can infer the reality of X, only when the latter is 

 not merely the sufficient or necessitating, but also the only possible 

 cause of the former. 



But it is obvious that we cannot bring any such independent 

 experimental processes to bear upon X, to determine if it be 

 real, unless we suppose it to be of a nature at least partially 

 known, i.e. to have some analogy with known causes, to be of 

 such a kind that we can deduce from it something else besides the 

 bare phenomenon for whose explanation it was postulated. If we 

 cannot draw any other inference from it except that ; if it is so 

 unique, so unknown to us otherwise, that all we can say about it 

 is that &quot; it is a something which is the determining cause of this 

 phenomenon &quot; ; if we cannot study it in varying sets of conditions, 

 and conceive what its effects would be, and how its influence 

 would be manifested therein, and see whether these inferences 

 tally with the phenomena that are observed to occur in these 

 conditions : if we cannot do all this, manifestly we cannot hope 

 to be able rigorously to verify our hypothesis ; for it is only by 

 doing all this that we can sift the surroundings of the pheno 

 menon and prove that the supposed cause, X, is the real one, by 

 proving that it is not only a sufficient (necessitating) cause, but 

 the only possible cause, that could determine or bring about the 

 phenomenon. Unless, for example, we supposed the so-called 

 luminiferous ether to resemble matter so far at least as to be sub 

 ject to the laws of motion, unless we supposed it to have some 



