82 -SCIENTIFIC METHOD IN PHILOSOPHY 



train coming, there is no very close causal connection 

 between my two sense-data ; but if I look at the moon 

 on two nights a week apart, there is a very close causal 

 connection between the two sense-data. The simplest, 

 or at least the easiest, statement of the connection is 

 obtained by imagining a " real " moon which goes on 

 whether I look at it or not, providing a series of possible 

 sense-data of which only those are actual which belong to 

 moments when I choose to look at the moon. 



But the degree of verification obtainable in this way is 

 very small. It must be remembered that, at our present 

 level of doubt, we are not at liberty to accept testimony. 

 When we hear certain noises, which are those we should 

 utter if we wished to express a certain thought, we 

 assume that that thought, or one very like it, has been in 

 another mind, and has given rise to the expression which 

 we hear. If at the same time we see a body resembling 

 our own, moving its lips as we move ours when we 

 speak, we cannot resist the belief that it is alive, and that 

 the feelings inside it continue when we are not looking at 

 it. When we see our friend drop a weight upon his 

 toe, and hear him say what we should say in similar 

 circumstances, the phenomena can no doubt be explained 

 without assuming that he is anything but a series of 

 shapes and noises seen and heard by us, but practically 

 no man is so infected with philosophy as not to be quite 

 certain that his friend has felt the same kind of pain as 

 he himself would feel. We will consider the legitimacy 

 of this belief presently ; for the moment, I only wish to 

 point out that it needs the same kind of justification as 

 our belief that the moon exists when we do not see it, 

 and that, without it, testimony heard or read is reduced 

 to noises and shapes, and cannot be regarded as evidence 

 of the facts which it reports. The verification of physics 



