xxxix.] MENTAL INTELLIGENCE. 



takes for granted that wliicli is to be explained. The 

 question is, how are we able to reason from the known to 

 the unknown ? — why we believe, and truly believe, that it 

 is practicable to apply data of experience to things of 

 which we have no experience ? And the answer is, that 

 we believe in the accustomed order of nature obtaining 

 among the things we do not know, because we are familiar 

 with it among the things that we do know. Surely this 

 is no explanation at all. It is worth while, however, to 

 look more closely into the question. To say that the 

 belief in the constancy of the order of things is due to 

 habit, is the same thing as to say that it is due to associa- 

 tion; for association is simply mental habit. Now, how 

 can the mere association between two ideas, of itself, pro- 

 duce a belief in the association between the corresponding 

 things ? No doubt it appears to do so, but this, I think, 

 is only because the axiom of the constancy of the order 

 of things is habitually and unconsciously assumed. For 

 what is the law of association ? As stated in a former 

 chapter, it is merely this : if any two things, such as 

 lightning and thunder, have been habitually united in our 

 experience, the ideas of them will become united in our 

 thoughts, so that if we see lightning we shall think of 

 thunder, and if we hear thunder we shall think of light- 

 ning. But the thoughts of lightning and of thunder are 

 mere impressions on the consciousness : and how can the 

 association between two mere impressions, however in- 

 separable it may be, engender the belief that the things 

 in the external world to which those impressions on the 

 consciousness correspond will be found in corresponding 

 association ? There is a step from thoughts to things, 

 from the association of ideas to a beKef in the association 

 of the things corresponding to the ideas, for which, I think, 

 no mere laws of habitual association will account. 



It may be said in reply to this, that, as a matter of fact, 

 belief is in many cases obviously determined by habit, 

 and by no other cause whatever. Most men have beliefs, 

 especially on religious and political subjects, which have 

 no ground wliatever except haljit, originating usually in 



