96 THE SCIENCE OF LOGIC 



but merely states that &quot; If such causes do exist and act thus, 

 they will always produce the same classes of effects &quot; 



It may, perhaps, be objected that we could not have formed the 

 notion of &quot;non-free causes &quot; at all, unless there were such causes 

 in the world revealed to us by our senses. This, however, is 

 scarcely so. The data of our sense knowledge must, of course, 

 have presented such uniformity as suggested the idea of &quot;non- 

 free &quot; causes to us. But we might conceivably have been mis 

 taken in adopting that suggestion, and judging that the causes of 

 those phenomena are really non-free : just as those philosophers 

 who deny free-will maintain that we are really mistaken in con 

 cluding from the facts of our own internal experience that we have 

 free-will. However this may be, the hypothetical statement of the 

 principle of uniformity evades this question of fact in regard to 

 non-free causes. The categorical statement of the same principle, 

 however, implies and asserts the fact of their actual existence. 



It is not, therefore, in the formal generalization of the abstract 

 principle in the assertion that &quot; If (whenever ; wherever, as often 

 as) any physical cause acts in the same circumstances, it will pro 

 duce similar effects &quot; that the difficulty lies, but in its material 

 generalization, i.e., (a) in asserting that there are and have been and 

 will be such causes in existence, and (b] in proving that the various 

 cases which we allege to be actual instances illustrative of the 

 principle are indeed such. 1 



In order, for instance, to be able to apply the abstract principle 

 of uniformity in (a) establishing by induction the general law 

 that &quot;an iron bar is lengthened by the application of heat,&quot; 2 and 

 in (ft) applying this law to any particular case, we must be able not 

 merely to assert the. formally general (hypothetical) principle that 

 &quot; natural or non-free causes produce the same results if they act 

 repeatedly in similar circumstances,&quot; but we must be able further 

 more to assert categorically (a) that heat acting on iron is such a 

 cause, and will therefore always lengthen an iron bar, and () that 

 this particular case is really a case of an iron bar acted on by heat. 



The general categorical assertion, that &quot; the causes which are at 

 work in the physical universe are non-free, or fixed by nature in their 

 mode of action, and that therefore they always have acted and always 



l cf. MERIER, Logique, p. 330. 



2 We assume here, with Mill, whatever about the conventions of formal logic, 

 that all such physical laws and general truths, reached by experience, imply the exist 

 ence or occurrence of the things and events to which they refer (cf. 128). 



