84 WHAT IS SCIENCE? 



even if the laws could not be deduced correctly ; they 

 would then offer an explanation, although the explanation 

 would not be true. 



And this is, I believe, the reason why he would feel thus. 

 Only those who have practised experimental physics, 

 know anything by actual experience about the laws of 

 gases ; they are not things which force themselves on 

 our attention in common life, and even those who are most 

 familiar with them never think of them out of working 

 hours. On the other hand, the behaviour of moving 

 solid bodies is familiar to every one ; every one knows 

 roughly what will happen when such bodies collide with 

 each other or with a solid wall, though they may not 

 know the exact dynamical laws involved in such reactions. 

 In all our common life we are continually encountering 

 moving bodies, and noticing their reactions ; indeed, 

 if the reader thinks about it, he will realize that whenever 

 we do anything which affects the external world, or when- 

 ever we are passively affected by it, a moving body is 

 somehow involved in the transaction. Movement is 

 just the most familiar thing in the world ; it is through 

 motion that everything and anything happens. And so 

 by tracing a relation between the unfamiliar changes 

 which gases undergo when their temperature or volume 

 is altered, and the extremely familiar changes which 

 accompany the motions and mutual reactions of solid 

 bodies, we are rendering the former more intelligible ; 

 we are explaining them. 



That is to say, the explanation of laws offered by 

 theories (for this example has been offered as typical) 

 is characteristically explanation of the first of the two 

 kinds with which the chapter started. It is explana- 

 tion by greater familiarity, essentially similar to that 

 offered when a statement is translated from an unknown 

 to a known language. This conclusion may be surprising, 

 and indeed it is not that generally advanced. Before 



