68 SCIENTIFIC METHOD IN PHILOSOPHY 



as an approximate truth, has acquired by this time the 

 same kind of certainty as the existence of Napoleon, 

 whereas the latest speculations concerning the constitu- 

 tion of matter would be universally acknowledged to 

 have as yet only a rather slight probability in their favour. 

 These varying degrees of certainty attaching to different 

 data may be regarded as themselves forming part of our 

 data ; they, along with the other data, lie within the 

 vague, complex, inexact body of knowledge which it is 

 the business of the philosopher to analyse. 



The first thing that appears when we begin to analyse 

 our common knowledge is that some of it is derivative, 

 while some is primitive ; that is to say, there is some 

 that we only believe because of something else from 

 which it has been inferred in some sense, though not 

 necessarily in a strict logical sense, while other parts are 

 believed on their own account, without the support of any 

 outside evidence. It is obvious that the senses give know- 

 ledge of the latter kind : the immediate facts perceived by 

 sight or touch or hearing do not need to be proved by 

 argument, but are completely self-evident. Psychologists, 

 however, have made us aware that what is actually given 

 in sense is much less than most people would naturally 

 suppose, and that much of what at first sight seems to be 

 given is really inferred. This applies especially in regard 

 to our space-perceptions. For instance, we instinctively 

 infer the "real" size and shape of a visible object from 

 its apparent size and shape, according to its distance and 

 our point of view. When we hear a person speaking, 

 our actual sensations usually miss a great deal of what he 

 says, and we supply its place by unconscious inference ; 

 in a foreign language, where this process is more difficult, 

 we find ourselves apparently grown deaf, requiring, for 

 example, to be much nearer the stage at a theatre than 



