128 THE SCIENCE OF LOGIC 



must we suppose our cause to be, in order that our supposition of 

 its existence be a scientific hypothesis ? 



The controversy as to what kind or concept of cause it is legiti 

 mate for us to employ in our hypotheses about the phenomena 

 of nature, is one of very long standing. No supposition of ours, 

 as to what is the cause of a phenomenon, will be of any use unless 

 it be verifiable. But what kind of cause must we suppose to be 

 operative, if our supposition is to be verifiable ? Newton insisted 

 that the object of our hypothesis must be a vera causa, a real 

 cause meaning, thereby, to exclude arbitrary, fanciful, a priori 

 suppositions and prejudices, not suggested by facts of experience. 

 This, of course, is obviously right and proper. Must the cause, 

 however, be supposed to be itself a phenomenon of some sort, i.e. 

 something itself perceptible by the senses, so that the only valid 

 verification of such hypothesis would be actual discovery, by sense 

 perception, of the supposed cause, and actual observation of its 

 visible causal connexion with the effect ? Such a requirement is 

 rightly repudiated by scientists, though it is only such a sort of 

 cause that answers to Mill s definition. 1 Followers of Mill s 

 phenomenist philosophy contend that it is a mere waste of time, 

 and a hindrance to real scientific progress, to refer the various 

 phenomena of mind, or of external nature, to corresponding 

 &quot; faculties &quot; or &quot; powers &quot; or &quot; forces &quot; in either domain. And 

 no doubt, such reference of individual effects, or classes of effects, 

 to corresponding efficient principles, whether these be called 

 &quot; faculties &quot; or &quot; forces,&quot; would be calculated to retard further in 

 vestigation, if such reference were taken as an ultimate rational 

 explanation of those effects ; if, for instance, men were so foolish 

 as to think they had said the last word as to why opium induces 

 sleep by declaring opium to have a vis dormativa to use the old 

 familiar example. 



It is true that in the Renaissance period some of the decadent camp-followers 

 of the great mediaeval Scholastics left themselves open to this reproach by taking 

 refuge in such verbal explanations of natural phenomena. 2 But up to quite 



1 Logic, III., v., 2. Cf. supra, p. 74, n. 3 ; infra, p. 131. 



2 C/. DE WULF, Scholasticism Old and New (2nd edition), pp. 147 sqq. ; His 

 tory of Medieval Philosophy, p. 503. It was not, however, the fault of those mediaeval 

 philosophers that the &quot; forces &quot; or &quot; causes &quot; in question were then, and are still for 

 the most part, &quot; occult,&quot; i.e. such that we have no positive imagination of the mode 

 of their action. Modern scientists who are loudest in their ridicule of those &quot; occult 

 forces &quot;are themselves obliged to have recourse to &quot; motions &quot; and &quot; masses &quot; and 

 &quot; ions&quot; and &quot; electrons &quot; and &quot; ids &quot; and &quot; biophors &quot; and a whole host of such things, 



