202 OPERATIONS SUBSIDIARY TO INDUCTION. 



do so, but of the art of intellectual Education. Our 

 business with Observation is only in its connexion 

 with the appropriate problem of logic, the estimation 

 of evidence. We have to consider, not how or what 

 to observe, but under what conditions observation is 

 to be relied on; what is needful, in order that the 

 factj supposed to be observed, may safely be received 

 as true. 



$ 2. The answer to this question is very simple, at 

 least in its first aspect. The sole condition is, that 

 what is supposed to have been observed shall really 

 have been observed; that it be an observation, not an 

 inference. For in almost every act of our perceiving 

 faculties, observation and inference are intimately 

 blended. What we are said to observe is usually a 

 compound result, of which one-tenth may be observa- 

 tion, and the remaining nine-tenths inference. 



I affirm, for example, that I hear a man's voice. 

 This would pass, in common language, for a direct per- 

 ception. All, however, which is really perception, is 

 that I hear a sound. That the sound is a voice, and 

 that voice the voice of a man, are not perceptions but 

 inferences. I affirm, again, that I saw my brother at a 

 certain hour this morning. If any proposition con- 

 cerning a matter of fact would commonly be said to be 

 known by the direct testimony of the senses, this surely 

 would be so. The truth, however, is far otherwise. I 

 only saw a certain coloured surface ; or rather I had the 

 kind of visual sensations which are usually produced 

 by a coloured surface; and from these as marks, known 

 to be such by previous experience, I concluded that I 

 saw my brother. I might have had sensations pre- 

 cisely similar, when my brother was not there. I 

 might have seen some other person so nearly resem- 



