SENSATION AND THE SENSIFEROUS ORGANS. 269 



said of any of the three that it is inconceivable, or that 

 it can be assumed on d priori grounds to be impossi- 

 ble. 



Consider the first, for example ; an immaterial sub- 

 stance is perfectly conceivable. In fact, it is obvious 

 that, if we possessed no sensations but those of smell 

 and hearing, we should be unable to conceive a material 

 substance. We might have a conception of time, but 

 could have none of extension, or of resistance or of mo- 

 tion. And without the three latter conceptions no idea 

 of matter could be formed. Our whole knowledge would 

 be limited to that of a shifting succession of immaterial 

 phenomena. But, if an immaterial substance may exist, 

 it may have any conceivable properties ; and sensation 

 may be one of them. All these propositions may be 

 affirmed with complete dialectic safety, inasmuch as they 

 cannot possibly be disproved ; but neither can a particle 

 of demonstrative evidence be offered in favour of the 

 existence of an immaterial substance. 



As regards the second hypothesis, it certainly is not 

 inconceivable, and therefore it may be true, that sensa- 

 tion is the direct effect of certain kinds of bodily motion. 

 It is just as easy to suppose this as to suppose, on the 

 former hypothesis, that bodily motion affects an imma- 

 terial substance. But neither is it susceptible of proof. 



And, as to the third hypothesis, since the logic of 

 induction is in no case competent to prove that events 

 apparently standing in the relation of cause and effect 

 may not both be effects of a common cause that also is 



