204 OPERATIONS SUBSIDIARY TO INDUCTION. 



by one object, I can hardly, if my eyes are shut, help 

 believing that there are two marbles instead of one. 

 Bat it is not my touch in this case, nor my sight in 

 the other, which is deceived; the deception, whether 

 durable or only momentary, is in my judgment. From 

 my senses I have only the sensations, and those are 

 genuine. Being accustomed to have those or similar 

 sensations when, and only when, a certain arrange- 

 ment of outward objects is present to my organs, I 

 have the habit of instantly, when I experience the 

 sensations, inferring the existence of that state of 

 outward things. This habit has become so powerful, 

 that the inference, performed with the speed and 

 certainty of an instinct, is confounded with intui- 

 tive perceptions. When it is correct, I am uncon- 

 scious that it ever needed proof; even when I know 

 it to be incorrect, I cannot without considerable effort 

 abstain from making it. In order to be aware that it 

 is not made by instinct but by an acquired habit, I 

 am obliged to reflect on the slow process by which I 

 learned to judge by the eye of many things which I 

 now appear to perceive directly by sight; and on the 

 reverse operation performed by persons learning to 

 draw, who with difficulty and labour divest themselves 

 of their acquired perceptions, and learn afresh to see 

 things as they appear to the eye, instead of seeing 

 them as they really are. 



It would be easy to prolong these illustrations, 

 were there any need to expatiate upon a topic so 

 copiously exemplified in various popular works. From 

 the examples already given, it is seen sufficiently, that 

 the individual facts from which we collect our induc- 

 tive generalizations are scarcely ever obtained by 

 observation alone. Observation extends only to the 

 sensations by which we recognize objects ; but the 



