FINAL CAl'SES. 25 



would shake the foundation of every kind of 

 knowledge, even that which we regard as built 

 upon the most solid basis. Of causation, it is 

 agreed that we know nothing ; all that we do 

 know is, that one event succeeds another with 

 undeviating constancy. Now, if we vrere to 

 probe this subject to the bottom, we should find 

 that, in rigid strictness, we have no certain 

 knowledge of *the existence of any thing, save 

 that of the ' sensations and ideas which are 

 actually passing in our minds, and of which we 

 are necessarily conscious. Our belief in the 

 existence of external objects, in their undergoing 

 certain changes, and in their possessing certain 

 physical properties, rests on a different founda- 

 tion, namely, the evidence of our senses ; for it 

 is the result of inferences which the mind is, by 

 the constitution of its frame, necessarily led to 

 form. We may trace to a similar origin the 

 persuasion, irresistibly forced upon us, that there 

 exist not only other material objects beside our 

 own bodies, but also other intellectual beings 

 beside ourselves. We can neither see nor feel 

 those extraneous intellects, any more than we 

 can see or feel the cause of gravitation, or the 

 subtle sources of electricity or magnetism. We 

 nevertheless believe in the reality both of the one 

 and of the other ; but it is only because we infer 

 their existence from particular trains of impres- 



