84 SCIENTIFIC METHOD IN PHILOSOPHY 



have ceased to be sensible for example, that the hard- 

 ness of a visible body, which has been discovered by 

 touch, continues when the body is no longer touched 

 may be replaced by the statement that the effects of 

 sensible objects persist, i.e. that what happens now can 

 only be accounted for, in many cases, by taking account 

 of what happened at an earlier time. Everything that 

 one man, by his own personal experience, can verify in 

 the account of the world given by common sense and 

 physics, will be explicable by some such means, since 

 verification consists merely in the occurrence of an ex- 

 pected sense-datum. But what depends upon testimony, 

 whether heard or read, cannot be explained in this way, 

 since testimony depends upon the existence of minds 

 other than our own, and thus requires a knowledge of 

 something not given in sense. But before examining 

 the question of our knowledge of other minds, let us 

 return to the question of the thing-in-itself, namely, to 

 the theory that what exists at times when we are not 

 perceiving a given sensible object is something quite 

 unlike that object, something which, together with us 

 and our sense-organs, causes our sensations, but is never 

 itself given in sensation. 



The thing-in-itself, when we start from common-sense 

 assumptions, is a fairly natural outcome of the difficulties 

 due to the changing appearances of what is supposed to 

 be one object. It is supposed that the table (for example) 

 causes our sense-data of sight and touch, but must, since 

 these are altered by the point of view and the intervening 

 medium, be quite different from the sense-data to which 

 it gives rise. There is, in this theory, a tendency to a 

 confusion from which it derives some of its plausibility, 

 namely, the confusion between a sensation as a psychical 

 occurrence and its object. A patch of colour, even if it 



