LAWS OF MIND. 441 



It is certain that the natural differences which really exist 

 in the mental predispositions or susceptibilities of different 

 persons, are often not unconnected with diversities in their 

 organic constitution. But it does not therefore follow that 

 these organic differences must in all cases influence the mental 

 phenomena directly and immediately. They often affect them 

 through the medium of their psychological causes. For 

 example, the idea of some particular pleasure may excite in 

 different persons, even independently of habit or education, 

 very different strengths of desire, and this may be the effect 

 of their different degrees or kinds of nervous susceptibility ; 

 but these organic differences, we must remember, will render 

 the pleasurable sensation itself more intense in one of these 

 persons than in the other; so that the idea of the pleasure will 

 also be an intenser feeling, and will, by the operation of mere 

 mental laws, excite an intenser desire, without its being neces- 

 sary to suppose that the desire itself is directly influenced by 

 the physical peculiarity. As in this, so in many cases, such 

 differences in the kind or in the intensity of the physical 

 sensations as must necessarily result from differences of bodily 

 organization, will of themselves account for many differences 

 not only in the degree, but even in the kind, of the other 

 mental phenomena. So true is this, that even different 

 qualities of mind, different types of mental character, will 

 naturally be produced by mere differences of intensity in the 

 sensations generally : as is well pointed out in an able essay 

 on Dr. Priestley, mentioned in a former chapter : 



" The sensations which form the elements of all knowledge 

 are received either simultaneously or successively ; when several 

 are received simultaneously, as the smell, the taste, the colour, 

 the form, &c. of a fruit, their association together constitutes 

 our idea of an object; when received successively, their 

 association makes up the idea of an event. Anything, then, 

 which favours the associations of synchronous ideas, will tend 

 to produce a knowledge of objects, a perception of qualities ; 

 while anything which favours association in the successive 

 order, will tend to produce a knowledge of events, of the 



