LAWS OF Mr\n. 533 



laws. And it is to be remarked, that the ease is not always one of 

 Composition of Causes: the eflect of concurrinir causes is not always 

 precisely the sum of the eflects of those causes when separate-, nor even 

 always an ett'ect of the same kind with them. Hevertin»? to the dis- 

 tinction which occupies so prominent a place in the theory of induc- 

 tion ; the laws of the phenomena of mind are sometimes analot^ous to 

 mechanical, but sometimes also to chemical laws. When many im- 

 pressions or ideas are operatinej in the mind together, th»'n! sometimes 

 takes place a process of a similar kind to chemical combination. 

 Wlien inipressii>ns have been so often experienced in conjunction, that 

 each of them calls up readily and instantaneously the ideas of the whole 

 group, those ideas sometimes tnelt and coalesce into one another, and 

 appear not several ideas but one ; in the same manner as when the 

 seven prismatic colors are jiresented to the eye in rapid siuxession, 

 the sensation produced is that of ^vhite. J^ut as in this bust case it is 

 correct to say that the seven colors when they rapidly follow one 

 another generate white, but not that they actually are. white; so it 

 appears to me that the Complex Idea, formed by the blending together 

 of several simpler ones, should, when it really appears simple, (that is 

 when the separate elements are not consciously distinguishable in it,) 

 be said to result from, or be getierated hi/, the simple ideas, not to cu/i- 

 sist of them. Our idea of an orange really consists of the simple ideas 

 of a certain color, a certain form, a certain taste and smell, &c., be- 

 cause we can by interrogating our consciousness, perceive all these ele- 

 ments in the idea. But we cannot perceive, in so apparently simple a 

 feeling as our perception of the shape of an object by the eye, all that 

 multitude of ideas derived from other senses, without which it is well 

 ascertained that no such visual perception would ever have had exist- 

 ence ; nor, in our idea of Extension, can we discover those elementary 

 ideas of resistance, derived from f)ur muscular frame, in which Dr. 

 Brown has rendered it highly probable that the idea originates. These 

 therefore are cases of mental chemistry : in which it is proper to say 

 that the simple ideas generate, rather than that they compose, the com- 

 plex ones. * 



With respect to all the other constituents of the mind, its beliefs, 

 its abstruser conceptions, its sentiments, emotions, and volitions ; there 

 are some (among whom are Hartley, and the author of the Analysis) 

 who think that the whole of these are [generated from simple ideas of 

 sensation, by a chemistry similar to that which we have just cxemj)li- 

 fied. I am unable to satisfy myself that this conclusion is, in the pres- 

 ent state of our knowledge, fully made out. In many cases I cannot 

 even perceive, that the line of argument adopted has much tendency 

 to establish it. The philosophers to whom I have referred have, in- 

 deed, conclusively .shown that there is such a thing as mental chemis- 

 try ; that the heterogeneous nature of a feeling. A, c(msidered iu 

 relation to B and C, is no conclusive argument against its being gener- 

 ated from B and C. Ha\-ing prove<l this, ihvy proceed to show, that 

 where A is found, B and C were, or may have been, present, and why 

 therefore, they say, should not A have been generated from B and C ] 

 But even if this evidence were canied to the highest degree of com- 

 pleteness which it admits of; if it wtjn; shown that certain groups of 

 associated ideas not only might have been, but actually were, present 

 whenever the raoro recondite mental feeling was exponenced ; tliis 



