CONCEPTS OF &quot; REASON &quot; AND &quot; CA USE &quot; 75 



but likewise the domain of human activity (201). Nor should he identify 

 physical science with science simply : &quot; If the non-mechanical conditions upon 

 which physical changes depend (supposing that such there are) cannot be as 

 certained and formulated in a way which enables physical science to take ac 

 count of them, it will treat them as non-existent. It is of no use to regard a factor, 

 whose mode of action is unascertainable. It must remain for science what the 

 will is upon one theory of human freedom a source of purely incalculable and 

 to it irrational interference. But irrational interference is just what cannot be 

 supposed to occur. No doubt an interference which admits an explanation 

 according to law is not irrational ; but if the law is unascertainable, it is as 

 good as irrational. And this attitude of physical science has the practical justi 

 fication, that if events are once admitted to occur in the material order whose 

 conditions are unascertainable within that order, there is no point at which we 

 can draw the line. Only by assuming that it can explain everything is it possible 

 to find out how much it can explain in physical terms.&quot; 1 For the credit of 

 physical science itself we should be sorry to find any of its students claim such 

 pretensions for it as the author here attempts to justify (201). The physical 

 scientist may, of course, legitimately abstract from the existence of &quot; non- 

 mechanical conditions,&quot; but he may not gratuitously deny their existence. 

 Surely, too, a &quot; factor &quot; may be &quot; unascertainable,&quot; in the sense of being 

 &quot; incalculable &quot; in terms of material atoms and motion, may not admit of 

 &quot; explanation according to &quot; mechanical &quot; law,&quot; and yet need not be, or 

 be called, &quot; irrational,&quot; or &quot; as good as irrational &quot;. Is that alone &quot;rational &quot; 

 which is &quot; mechanical &quot; ? or is there no &quot; law,&quot; no &quot; explanation,&quot; for what 

 is not mechanical ? Surely this is a vast and gratuitous assumption for 

 anyone to make, whether in the name of physical science or on any other 

 pretext. We fail to see why the physical scientist must deny that &quot; events &quot; 

 may and do &quot; occur in the material order whose conditions are unascertainable 

 within that order &quot;. The man who ventures on such a denial would evince 

 more daring than science. Finally, can science &quot; find out how much it can 

 explain &quot; only &quot; by assuming that it can explain everything &quot; ? Again we 

 must confess our failure to see the necessity of any such extraordinary 

 assumption. 



Bearing those few cautions in mind, we may now glance at the growth of 

 some prevalent views about physical causality. 



219. THE SENSIST OR EMPIRICAL VIEW OF CAUSALITY: 

 MILL S TEACHING. John Locke (1632-1704) had taught that 

 causality, or the power to produce change, was not &quot; contained 

 in the real existence of things, but . . . extraneous and super 

 induced &quot; i.e. by the consideration of the mind. But causality 

 in things seems to be as real as their substantiality, nay, as their 

 very existence. Accordingly, either causality is real or all 

 reality is simply a subjectively fabricated idea. The latter alter 

 native was practically accepted by David Hume (1711-1776), 

 who reduced all reality to a series of subjective feelings or states 



l op. cit., p. 386. 



