262 SENSATION AND THE SENSIFEROUS ORGANS. [LECT. 



tenacity and advocated with passion. I do not think 

 it can be said of any of the three that it is inconceiv- 

 able, or that it can be assumed on d, priori grounds 

 to be impossible. 



Consider the first, for example ; an immaterial 

 substance 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 resist- 

 ance, or of motion. And without the three latter 

 conceptions no idea of matter could be formed. Our 

 whole knowledge would be limited to that of a shift- 

 ing 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 

 sensation is the direct effect of certain kinds of bodily 

 motion. It is just as easy to suppose this as to sup- 

 pose, on the former hypothesis, that bodily motion 

 affects an immaterial 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 



