XXXVI.] PERCEPTION. 129 



quite conceivable that in a different world from tliis, a 

 mental natiu-e as highly developed as ours might he evolved 

 out of the germ of a single sense, at least if that sense 

 were sight ; and to such a being the nature of perception 

 would probably present no difficulty whatever. 



I think I have shown in this chapter that what Ave call Elements 

 perception, and naturally regard as a single mental act, iu^perce^j- 

 really consists of distinct elements, which may be thus tio" enu- 



, T merated. 



enumerated : — 



1. The referring of a sensation to its source ; as when Assign- 

 we recognise a voice as that of a friend, or, in other words, sensation 

 perceive the friend by means of his voice. This has not to its 

 necessarily anything to do with the cognition of space. It ^°'^^°®" 

 is true we know that every sound must come from some 

 place, but it is not by means of the sense of hearing that 



we have learned this. Had we no sense except hearing, 

 we should have no cognition of sjDace at all. 



2. The cognition of space-relations between our sensa- Cognition 

 tions : and - of space- 

 mi • • n 1 • 1 T relations. 



3. The cognition of a third dimension m space by means 



of the motor or muscular sense. 



4. Having learned to refer a sensation to a source, and Percep- 

 having acquired the cognition of space in three dinien- objects in 

 sions, we become able to perceive the source of a sensation space. 



in external space ; that is to say, to perceive objects 

 external to the body. 



5. Lastly, we learn to combine the impressions of sight Combina- 

 with those of touch, and thus to acquire the very comiolex ^°^ °^ 



^ J ± impres- 



ideas that we have of external objects. sions of 



I believe that by thus separating the complex subject of g°,^^j^^. 

 perception into its elements, we remove the difficulties 

 which have hung round it, and make it as explicable as 

 any mental function can be. 



One cause of difficulty concerning the present subject is 

 the ambiguity of the expression " the external world." 

 What is this understood to be external to ? Is it to the ^'^lat is 



" the 



mind, or only to the body ? In other words, is the body external 

 part of the external world ? This question may appear to "^^^''^"^ "' 

 be only a verbal one ; and we may appear to dispose of it to 



VOL II. K 



