572 LOGIC OF THE MORAL SCIENCES. 



than that constituted by the two counter-motives 

 already specified. Not that any political economist 

 was ever so absurd as to suppose that mankind are 

 really thus constituted, but because this is the mode 



' in which science must necessarily proceed. When an 

 effect depends upon a concurrence of causes, these 

 causes must be studied one at a time, and their laws 

 separately investigated, if we wish, through the causes, 

 to obtain the power of either predicting or controlling 

 the effect; since the law of the effect is compounded 



upf the laws of all the causes which determine it. The 

 law of the centripetal and that of the tangential force 

 must have been known, before the motions of the 

 earth and planets could be explained, or many of 

 them predicted. The same is the case with the con- 



r duct of man in society. In order to judge how he 

 will act under the variety of desires and aversions 

 which are concurrently operating upon him, we must 

 know how he would act under the exclusive influence 



of each one in particular. There is, perhaps, no action 

 of a man's life in which he is neither under the imme- 

 diate nor under the remote influence of any impulse 

 but the mere desire of wealth. There are many parts 

 of human conduct of which wealth is not even the 

 principal object, and to these political economy does 

 not pretend that its conclusions are applicable. But 

 there are also certain departments of human affairs, in 

 which the acquisition of wealth is the main and ac- 

 knowledged end. It is only of these that political 

 economy takes notice. The manner in which it 

 necessarily proceeds is that of treating the main and 

 acknowledged end as if it were the sole end; which, 

 of all hypotheses equally simple,, is the nearest to the 

 truth. The political economist inquires, what are the 

 actions which would be produced by this desire, if 



