8 INTRODUCTION. 



estimate of the object's distance from us is the result 

 of a comparison (made with so much rapidity that 

 we are unconscious of making it) between the size 

 and colour of the object as they appear at the time, 

 and the size and colour of the same or of similar 

 objects as they appeared when close at hand, or 

 when their degree of remoteness was known by other 

 evidence. The perception of distance by the eye, 

 which seems so like intuition, is thus, in reality, an 

 inference grounded on experience; an inference, too, 

 which we learn to make ; and which we make with 

 more and more correctness as our experience increases; 

 though in familiar cases it takes place so rapidly as to 

 appear exactly on a par with those perceptions of sight 

 which are really intuitive,, our perceptions of colour*. 

 Of the science, therefore, which expounds the 

 operations of the human understanding in the pursuit 

 of truth, one essential part is the inquiry: What are 

 the truths which are the objects of intuition or con- 

 sciousness, and what are those which we merely infer? 

 But this inquiry has never been considered a portion 

 of logic. Its place is in another and a perfectly dis- 

 tinct department of science^ which may be called the 

 higher or transcendental metaphysics. For such is 

 the title which has been given to that portion of 

 mental philosophy which attempts to determine what 

 part of the furniture of the mind belongs to it origi- 

 nally, and what part is constructed by itself out of 



* This celebrated theory has recently been called in question by 

 a writer of deserved reputation, Mr. Samuel Bailey; but I do not 

 conceive that the grounds on which it has been received by phi- 

 losophers for a century past, have been at all shaken by that gentle- 

 man's objections. I have elsewhere said what appeared to me 

 necessary in reply to his arguments. Westminster Review, for 

 October, 1842. 



