92 HUME m 



and perception. If you pretend, therefore, to prove, a 

 priori, that such a position of bodies can never cause 

 thought, because, turn it which way you will, it is nothing 

 but a position of bodies : you must, by the same course of 

 reasoning, conclude that it can never produce motion, since 

 there is no more apparent connection in the one than in the 

 other. But, as this latter conclusion is contrary to evident 

 experience, and as 'tis possible we may have a like experience 

 in the operations of the mind, and may perceive a constant 

 conjunction of thought and motion, you reason too hastily 

 when, from the mere consideration of the ideas, you con- 

 clude that 'tis impossible motion can ever produce thought, 

 or a different position of parts give rise to a different pas- 

 sion or reflection. Nay, 'tis not only possible we may have 

 such an experience, but 'tis certain we have it ; since every 

 one may perceive that the different dispositions of his body 

 change his thoughts and sentiments. And should it be said 

 that this depends on the union of soul and body, I would 

 answer, that we must separate the question concerning the 

 substance of the mind from that concerning the cause of its 

 thought ; and that, confining ourselves to the latter ques- 

 tion, we find, by the comparing their ideas, that thought and 

 motion are different from each other, and by experience, 

 that they are constantly united ; which, being all the cir- 

 cumstances that enter into the idea of cause and effect, 

 when applied to the operations of matter, we may certainly 

 conclude that motion may be, and actually is, the cause of 

 thought and perception." (I. pp. 314-316.) 



The upshot of all this is, that the " collection 

 of perceptions," which constitutes the mind, is 

 really a system of effects, the causes of which are to 

 be sought in antecedent changes of the matter of 

 the brain, just as the "collection of motions," 

 which we call flying, is a system of effects the 



