FINAL CAUSES. 21 



sense is a very limited one. Those who urge it, do 

 not seem to be aware that its general application, in 

 that very same sense, would skake the foundation 

 of every kind of knowledge, even that which we 

 regard as built on the most solid basis. Of causa- 

 tion, it is agreed that we know nothing ; all that we 

 do know is, that one event succeeds another with un- 

 deviating constancy. Now by probing this subject 

 to the bottom, we shall 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 undergo- 

 ing certain changes, and in their possessing certain 

 physical properties, rests on a different foundation, 

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

 result of inferences which the mind is, by the con- 

 stitution of its frame, necessarily led to form. We 

 may trace to a similar origin the persuasion, irre- 

 sistibly 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 gra- 

 vitation, or the subtle sources of electricity and 

 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 impressions made upon our senses, of 

 which impressions alone our knowledge can, in 

 metaphysical strictness, be termed certain. 



Upon what evidence do I conclude that I am 

 not a solitary being in the universe ; that all is not 



