SCIENCE AND NATURE 17 



the position is intensified because all our habitual language 

 is based on the assumption that there is an external 

 world which we perceive. For instance, when I want 

 to call attention to the sensation of sound, I can only say 

 that " I hear a noise " ; but the very form of the words 

 which have to be used to convey my meaning imply that 

 the " noise" is something different from the "I," who 

 hears it. Nevertheless it is necessary to try to under- 

 stand how such doubts can be put forward. 



They are based on the fact that the experience of 

 seeing an object or hearing a sound is an event which 

 takes place in my mind ; it is a kind of thought if we 

 use the word " thought " to mean anything that goes 

 on in my mind. That fact is expressed when it is said 

 that " I " hear the noise. Though the noise may be the 

 same, the fact that " I " hear it is different from the fact 

 that "you" hear it; the first fact is something that 

 happens in "my" mind, the second something that happens 

 in " your" mind. The noise, or the thing that causes the 

 noise, may be something in the world of nature, external 

 to both you and me ; but the hearing of the noise, which 

 is the fact on which you and I base the conclusion that 

 there is a noise or that there is an external object making 

 a noise, that hearing is not something external ; it is 

 something internal to you or to me, according as you or 

 I hear it. This view, that the perception of an external 

 object is something internal to the person who perceives 

 it, is as much part of the common-sense attitude towards 

 the matter as the view that the perception gives evidence 

 of an external object. 



But now we may argue thus. It is agreed that the 

 perception of an external object is something internal to 

 the perceiver ; it is one of the thoughts, or the mental 

 events, of the perceiver. On the other hand we do not 

 regard all thoughts of a perceiver as giving evidence of 

 an external world ; there are also thoughts which are 



