450 OPERATIONS SUBSIDIAEY TO INDUCTION. 



is only in its connection with the appropriate problem of logic, the estima- 

 tion 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 fact, supposed to be observed, may safely be received as 

 true. 



§ 2. The answer to this question is very simple, at least in its first as- 

 pect. 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 infer- 

 ence are intimately blended. What we are said to observe is usually a 

 compound result, of which one-tenth may be observation, and the remain- 

 ing nine-tenths inference. 



I affirm, for example, that I hear a man's voice. This would pass, in com- 

 mon language, for a direct perception. All, however, which is really per- 

 ception, 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 di- 

 rect testimony of the senses, this surely would be so. The truth, however, 

 is far otherwise. I only saw a certain colored surface ; or rather I had the 

 kind of visual sensations which are usually produced by a colored surface ; 

 and from these as marks, known to be such by previous experience, I con- 

 cluded that I saw my brother. I might have had sensations precisely sim- 

 ilar, when my brother was not there. I might have seen some other per- 

 son so nearly resembling him in appearance, as, at the distance, and, with 

 the degree of attention which I bestowed, to be mistaken for him. I might 

 have been asleep, and have dreamed that I saw him ; or in a state of nerv- 

 ous disorder, which brought his image before me in a waking hallucina- 

 tion. In all these modes, many have been led to believe that they saw per- 

 sons well known to them, who were dead or far distant. If any of these 

 suppositions had been true, the affirmation that I saw my brother M^ould 

 have been erroneous; but whatever was matter of direct perception, name- 

 ly the visual sensations, would have been real. The inference only would 

 have been ill grounded ; I should have ascribed those sensations to a wrong 

 cause. 



Innumerable instances might be given, and analyzed in the same manner, 

 of what are vulgarly called errors of sense. There are none of them prop- 

 erly errors of sense; they are erroneous inferences from sense. When I 

 look at a candle through a multiplying glass, I see what seems a dozen 

 candles instead of one ; and if the real circumstances of the case were skill- 

 fully disguised, I might suppose that there were really that number ; there 

 would be what is called an optical deception. In the kaleidoscope there 

 really is that deception ; when I look through the instrument, instead of 

 what is actually there, namely a casual arrangement of coloi-ed fragments, 

 the appearance presented is that of the same combination several times re- 

 peated in symmetrical arrangement round a point. The delusion is of course 

 effected by giving me the same sensations which I should have had if such a 

 symmetrical combination had really been presented to me. If I cross two 

 of my fingers, and bring any small object, a marble for instance, into con- 

 tact with both, at points not usually touched simultaneously by one object, 

 I can hardly, if my eyes are shut, help believing that there are two marbles 

 instead-of one. But it is not my touch in this case, nor my sight in the 



