LAW OF CAUSATION. 261 



tion, no relation a priori^ between a motion and a thought. And as the 

 Cartesians, more than any other school of philosophical speculation before 

 or since, made their own minds the measure of all things, and refused, on 

 principle, to believe that Nature had done what they were unable to see 

 any reason why she must do, they affirmed it to be impossible that a ma- 

 terial and a mental fact could be causes one of another. They regarded 

 them as mere Occasions on which the real agent, God, thought fit to exert 

 his power as a Cause. When a man wills to move his foot, it is not his 

 will that moves it, but God (they said) moves it on the occasion of his 

 will. God, according to this system, is the only efficient cause, not qud 

 mind, or qud endowed with volition, but qud omnipotent. This hypoth- 

 esis was, as I said, originally suggested by the supposed inconceivability 

 of any i-eal mutual action between Mind and Matter ; but it was afterward 

 extended to the action of Matter upon Matter, for on a nicer examination 

 they found this inconceivable too, and therefore, according to their logic, 

 impossible. The deus ex machind was ultimately called in to produce a 

 spark on the occasion of a flint and steel coming together, or to break an 

 eg% on the occasion of its falling on the ground. 



All this, undoubtedly, shows that it is the disposition of mankind in gen- 

 eral, not to be satisfied with knowing that one fact is invariably anteced- 

 ent and another consequent, but to look out for something which may seem 

 to explain their being so. But we also see that this demand may be com- 

 pletely satisfied by an agency purely physical, provided it be much more 

 familiar than that which it is invoked to explain. To Thales and Anaxim- 

 enes, it appeared inconceivable that the antecedents which we see in nature 

 should produce the consequents ; but perfectly natural that water, or air, 

 should produce them. The writers whom I oppose declare this inconceiv- 

 able, but can conceive that mind, or volition, is per se an efficient cause : 

 while the Cartesians could not conceive even that, but peremptorily de- 

 clared that no mode of production of any fact whatever was conceivable, 

 except the direct agency of an omnipotent being; thus giving additional 

 proof of what finds new confirmation in every stage of the history of sci- 

 ence : that both what persons can, and what they can not, conceive, is very 

 much an affair of accident, and depends altogether on their experience, and 

 their habits of thought; that by cultivating the requisite associations of 

 ideas, people may make themselves unable to conceive any given thing ; 

 and may make themselves able to conceive most things, however inconceiv- 

 able these may at first appear ; and the same facts in each person's mental 

 history which determine what is or is not conceivable to him, determine 

 also which among the various sequences in nature will appear to him so 

 natural and plausible, as to need no other proof of their existence ; to be 

 evident by their own light, independent equally of experience and of ex- 

 planation. 



By what rule is any one to decide between one theory of this descrip- 

 tion and another ? The theorists do not direct us to any external evidence ; 

 they appeal each to his own subjective feelings. One says, the succession 

 C B appears to me more natural, conceivable, and credible per se, than the 

 succession A B ; you are therefore mistaken in thinking that B depends 

 upon A ; I am certain, though I can give no other evidence of it, that C 

 comes in between A and B, and is the real and only cause of B. The oth- 

 er answers, the succession^ C B and A B appear to me equally natural and 

 conceivable, or the latter more so than the former : A is quite capable of 

 producing B without any other intervention. A third agrees with the first 



