Sensations Compared. 191 



know how difficult the work is. Even In regard to 

 our sensations, or sense-perceptions, we can never 

 be sure that ours correspond with those of another 

 person, under the same conditions. You and your 

 friend look at a flower, and agree that it is yellow ; 

 but it does not follow that you both have the same 

 color-sensation. It simply follows, that each of you 

 has the same sensation, that has been produced in 

 him, by all objects which he has been taught to call, 

 yellow. But, as a matter of fact, when your friend 

 says he perceives a yellow color, he may have just 

 the same sensation, as you have, when you call the 

 color, blue. It is not probable that it is so, but it 

 is not possible for the best physicist, or metaphy- 

 sician in the world, to so make the comparison, as 

 to be sure that two persons have sensations alike, 

 when they give the same name to the sensations. 

 There is, indeed, one strong argument against the 

 likenessof sensations, which bear the same name, in 

 different individuals ; that is, the different effect of 

 these sensations upon the sensibilities. Two per- 

 sons agree as to a color ; but one likes it, another 

 dislikes it. They agree as to the name of an odor 

 or taste ; but they disagree, as to the effect of that 

 odor or taste, upon themselves. It is certainly a 

 fair question ; Does not the different effect of a 

 taste, or odor, or color, on different individuals, im- 

 ply that each produces a different sensation upon 

 one person from what it does upon another ? These 

 inquiries are started here, to show the inherent dif- 

 ficulty of comparing the sensations and mental oper- 

 ations of different individuals, if one is disposed to 



