594 LOGIC OF THE MORAL SCIENCES. 



mental phenomena contends foi* could be proved, we should not be the 

 more enabled to resolve the laws of the more complex feelings into those 

 of the simpler ones. The generation of one class of mental phenomena 

 from another, whenever it can be made out, is a highly interesting fact in 

 psychological chemistry; but it no more supersedes the necessity of an 

 experimental study of the generated phenomenon, than a knowledge of the 

 properties of oxygen and sulphur enables us to deduce those of sulphuric 

 acid without specific observation and experiment. Whatever, therefore, 

 may be the final issue of the attempt to account for the origin of our judg- 

 ments, our desires, or our volitions, from simpler mental phenomena, it is 

 not the less imperative to ascertain the sequences of the complex phenom- 

 ena themselves, by special study in conformity to the canons of Induction. 

 Thus, in respect to Belief, psychologists will always have to inquire what 

 beliefs we have by direct consciousness, and according to what laws one 

 belief produces another ; what are the laws in virtue of which one thing is 

 recognized by the mind, either rightly or erroneously, as evidence of an- 

 other thing. In regard to Desire, they will have to examine what objects 

 we desire naturally, and by what causes we are made to desire things 

 originally indifferent, or even disagreeable to us ; and so forth. It may be 

 remarked that the general laws of association prevail among these more 

 intricate states of mind, in the same manner as among tlie simpler ones. 

 A desire, an emotion, an idea of the higher order of abstraction, even our 

 judgments and volitions, when they have become habitual, are called up by 

 association, according to precisely the same laws as our simple ideas. 



§ 4. In the course of these inquiries, it will be natural and necessary to 

 examine how far the production of one state of mind by another is influ- 

 enced by any assignable state of body. The commonest observation shows 

 that different minds are susceptible in very different degrees to the action 

 of the same psychological causes. The idea, for example, of a given desira- 

 ble object will excite in different minds very different degrees of intensity 

 of desire. The same subject of meditation, presented to different minds, 

 will excite in them very unequal degrees of intellectual action. These 

 differences of mental susceptibility in different individuals may be, first, 

 original and ultimate facts ; or, secondly, they may be consequences of the 

 previous mental history of those individuals ; or, thirdly and lastly, they 

 may depend on varieties of physical organization. That the previous men- 

 tal history of the individuals must have some share in producing or in 

 modifying the whole of their mental character, is an inevitable conse- 

 quence of the laws of mind ; but that differences of bodily structure also 

 co-operate, is the opinion of all physiologists, confirmed by common experi- 

 ence. It is to be regretted that hitherto this experience, being accepted in 

 the gross, without due analysis, has been made the groundwork of empiric- 

 al generalizations most detrimental to tlie progress of real knowledge. 



It is certain that the natural differences which really exist in the mental 

 predispositions or susceptibilities of different persons are often not uncon- 

 nected 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 independ- 

 ently of habit or education, very different sti'engths of desire, and this may 

 be the effect of their different degrees or kinds of nervous susceptibility; 



