INTRODUCTION. 



the other ; must be in the number of 

 the primitive data, or of the conclu- 

 sions which can be drawn from these. 

 With the original data, or ultimate 

 premises of our knowledge; with their 

 number or nature, the mode in which 

 they are obtained, or the tests by 

 which they may be distinguished ; 

 logic, in a direct way at least, has, 

 in the sense in which I conceive the 

 science, nothing to do. These ques- 

 tions are partly not a subject of 

 science at all, partly that of a very 

 different science. 



Whatever is knovvTi to us by con- 

 sciousness, is known beyond possibility 

 of question. What one sees or feels, 

 whether bodily or mentally, one can- 

 not but be sure that one sees or feels. 

 No science is required for the purpose 

 of establishing such truths ; no rules 

 of art can render our knowledge of 

 them more certain than it is in itself. 

 There is no logic for this portion of 

 our knowledge. 



But we may fancy that we see or 

 feel what we in reality infer. A 

 truth, or supposed truth, which is 

 really the result of a very rapid in- 

 ference, may seem to be apprehended 

 intuitively. It has long been agreed 

 by thinkers of the most opposite 

 schools, that this mistake is actually 

 made in so familiar an instance as 

 that of the eyesight. There is nothing 

 of which we appear to ourselves to 

 be more directly conscious, than the 

 distance of an object from us. Yet it 

 has long been ascertained, that what 

 is perceived by the eye, is at most 

 nothing more than a variously coloured 

 surface ; that when we fancy we see 

 distance, all we really see is certain 

 variations of apparent size, and de- 

 grees of faintness of colour ; that our 

 estimate of the object's distance from 

 us is the result partly of a rapid in- 

 ference from the muscular sensations 

 accompanying the adjustment of the 

 focal distance of the eye to objects 

 unequally remote from us, and partly 

 of a comparison (made with so much 

 rapidity that we are unconscious of 

 :piaking 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 ap- 

 peared 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 experi- 

 ence 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 pex'ceptions 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 facts which are the 

 objects of intuition or consciousness, 

 and what are these which we merely 

 infer? But this inquiry has never 

 been considered a portion of logic. 

 Its place is in another and a perfectly 

 distinct department of science, to 

 which the name metaphysics more 

 particularly belongs : that portion of 

 mental philosophy which attempts to 

 determine what part of the furniture 

 of the mind belongs to it originally, 

 and what part is constructed out of 

 materials furnished to it from without. 

 To this science appertain the great 

 and much debated questions of the 

 existence of matter ; the existence of 

 spirit, and of a distinction between it 

 and matter ; the reality of time and 

 space, as things without the mind, 

 and distinguishable from the objects 

 which are said to exist in them. For 

 in the present state of the discussion 



* This important theory has of late 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 admitted as an established 

 doctrine for a century past, have been at 

 all shaken by that gentleman's objections. 

 I have elsewhere said what appeared to, 

 me necessary in reply to his arguments. 

 (Westminster Review for October 1842; re- 

 printed iu Dissertations and Discussions^ 



vol, a.) 



