XXXVI.] PERCEPTION. 119 



conscious oue. This is true — at least it is true iu the case 

 just supposed ; but the unconsciousness of a mental process 

 is a result of its being habitually performed. We can 

 perceive by sound, as accurately as the dog can percei^'e 

 by smell, and we can perceive the presence of our friends 

 by their voices ; but this is altogether an acquired per- 

 ception, depending on habitual association : when we are 

 learning to know a man by his voice, the power of iden- 

 tifying him graduates from hesitating inference to unhesi- 

 tating perception ; and when it has become perception, 

 it is accompanied by no more conscious thought than the 

 spontaneous perceptions of an animal. And when in- 

 ferences — that is, what are indisputably inferences — are 

 performed at once, spontaneously, and without effort, we 

 habitually speak of them as perceptions. David perceived 

 that his child was dead, when he saw the servants whisper. 



I believe this account of perception in itself presents The 

 no difficulties. I believe the difficulties with which ^ggi^f^^t" 

 the question is generally surrounded do not arise from plicated by 

 any metaphysical perplexity in the nature of the sub- questions. 

 ject itself, but from its being complicated with other 

 questions which come before us in connexion with it. 

 These questions concern the relation of the mind to space, 

 and the relation of the two senses of sight and touch to 

 each other in the act of j)erception ; so that in the treat- 

 ment of the theory of perception various questions have 

 got mixed up together, concerning the nature of that act 

 by which the mind refers sensations to their sources, the 

 nature and origin of the cognition of space, and the mode 

 in which the sensations of sight and touch are combined 

 in the perception of bodies. To these three distinct 

 inquiries some writers add a fourth, namely, the nature 

 of the idea of material substances as distinguished from 

 their properties. It is no wonder if four such questions 

 appear inextricably perplexed when they are all mixed 

 up together, and yet may prove to be manageable enough 

 if they are taken separately. 



I have stated my belief that perception is to be defined 



