CHAPTER II 



SCIENCE AND NATURE 



WHY DO WE BELIEVE IN AN EXTERNAL WORLD? 



HOW do we come to have any knowledge at all 

 of the external world of nature ? The answer 

 is obvious. We learn about the external world 

 through our senses, the senses of sight, hearing, and 

 touch, and, to a less degree, those of taste and smell 

 Everything that we know about the external world 

 comes to us from this source ; if we could neither see, 

 hear, nor feel, we should know nothing of what was 

 going on round about us, we should not even know that 

 there was anything going on round about us ; we probably 

 should not even form the idea that there is such a thing 

 as the external world. 



So much is clear and indubitable. But now we have 

 to ask a much more difficult question, and one concerning 

 which there has been much more difference of opinion. 

 Why do we regard our senses as giving us knowledge of 

 the external world ? Every one agrees that if we have 

 any knowledge of such a world, it is derived from what 

 we see, hear, and feel, and not from any other source ; 

 but it is quite possible to doubt that what we see, hear,' 

 and feel, does really give us that knowledge, or that we 

 are right in interpreting the evidence which we derive 

 from our senses in the manner in which we do habitually 

 interpret it. It is rather difficult for those who are 

 unfamiliar with the controversies that have raged round 

 this matter to grasp the position of those who express 

 such doubts ; it seems to us so obvious that when we 

 hear a noise or see an object we are perceiving something 

 external to ourselves. And the difficulty of grasping 



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