THE FACTS OF SCIENCE 49 



a limited group of immediate sense-impressions. I see 

 the shape, size, and colour of the blackboard, and I 

 assume that I shall find it hard and heavy. But here the 

 assumed properties are capable of being put to the direct 

 test of immediate sense-impression. I can touch and lift 

 the blackboard and complete my analysis of its properties. 

 Even the Capitol in Washington, of which I have had no 

 direct sense-impression, is capable of being put to the 

 same sort of direct test. Another man's consciousness, 

 however, can never, it is said, be directly perceived by 

 sense-impression, I can only mfer its existence from the 

 apparent similarity of our nervous systems, from observing 

 the same hesitation in his case as in my own between 

 sense -impression and exertion, and from the similarity 

 between his activities and my own. The inference is 

 really not so great as the metaphysicians would wish 

 us to believe. It is an inference ultimately based on 

 the physical fact of the interval between sense-impression 

 and exertion ; and though we cannot as yet physically 

 demonstrate another person's consciousness, neither can 

 we demonstrate physically that earth-grown apples would 

 fall at the surface of the planet of a fixed star, nor that 

 atoms really are component parts in the structure of 

 matter. It may be suggested that if our organs of sense 

 were finer, or our means of locomotion more complete, we 

 might be able to see atoms or to carry earth-grown apples 

 to a fixed star — in other words, to test physically, or by 

 immediate sense-impression, these inferences. But : — 



" When I come to the conclusion that you are conscious, 

 and that there are objects in your consciousness similar to 

 those in mine, I am not inferring any actual or possible 

 feelings of my own, but your feelings, which are not, and 

 cannot by any possibility become, objects in my con- 

 sciousness." ^ 



To this it may be replied, that, were our physiological 

 knowledge and surgical manipulation sufficiently complete, 

 it is conceivable that it would be possible for me to lae 



1 W. K. Clifford, "On the Nature of Things-in-Themselves," Z-et/?<r^j 

 and Essays, vol. ii. p. 72. 



4 



