THE THKOUY OF SENSATION*. 183 



who also denies that the states of mind in sensation are influenced 

 by the states of the body, accounts for the phenomena by a pre- 

 established harmony. It is sufficient to say in reply, that not only 

 is this theory, like the fonner one, without evidence, but that it con- 

 tradicts itself; for if my sensations are not caused by external 

 objects, they would have been just what they are, were there no 

 external world in existence. What evidence then have I that there t« 

 an external world, and what becomes of the pre-established har- 

 mony between it and the world of mind ? Other philosophers, 

 admitting the connexion to exist, by their industry in accounting 

 for the transfer of the impression along the nerves till these com- 

 municate the impulse to the brain, the immediate presence chamber 

 of the soul, seem as though they regarded it possible to explain the 

 action of matter on the mind by impulse, and, therefore, by con- 

 tact, in the same maimer as body acts on body. Sir Isaac 

 Newton says — " It is inconceivable that mere brute matter 

 should, without the intervention of something else, operate upon and 

 affect other matter without mutual contact." Hartley says that 

 impulse, understanding impulse by contact, is the only way by 

 which body acts on body ; and on such analogies it seems to have 

 been supposed (especially by the ancients) that the images of things 

 must be brought into innnediate contact with, and act by impulse on 

 the mind. On this I observe — 



First. — That the premises are false, it being now pretty well 

 established that there is no such thing as actual contact in the 

 universe. 



Secondly. — That were the premises true, the conclusion would 

 not follow, for we are not at liberty, as we have before remarked, to 

 reason from the laws of matter to those of mind, and to argue that 

 what is true of the latter, must be true of the fonner also. But, 



Thirdly. — Were both premises and conclusion correct, the great 

 mystery would yet be unexplained in either case. If the action is by 

 impulse, how is it that impulse produces the effect ? As Dugald 

 Stewart has well insisted, the communication of motion by impulse 

 is «p3 unaccountable as any other mystery. If this be the case with 

 matter, much more so with mind, the phenomena of which the action 

 of body is adduced to explain. 



This leads me to my last remark on these hypotheses, that they 

 all seem to originate in the idea that the connexion between matter 

 and mind is very much more inexplicable than any other. We think 

 we perfectly understand how matter acts on matter, but that the 

 influence of matter on mind is a great mystery. But are we not 

 equally ignorant in both cases ? Mankind have ever been anxious 

 to pry into the secret operations of nature, to discover the hidden 

 causes of events. "Felix qui potuit rerum cognoscere causas," has 

 been the sentiment of thinking minds in all ages. Yet after all the 

 researches of science, of the true efficient causes of things, nothing is 

 known. That there is some true eflSciency we have an intuitive belief, 

 but what this is in any case, is beyond the sphere of our observation. 

 We know nothing but links in the succession of events. The discovery 



