106 SCIENTIFIC METHOD IN PHILOSOPHY 



The time has hardly come when we can state precisely 

 what this legitimate conception is, but we can see in a 

 general way what it must be like. For this purpose, it 

 is only necessary to take our ordinary common-sense 

 statements and reword them without the assumption of 

 permanent substance. We say, for example, that things 

 change gradually sometimes very quickly, but not with- 

 out passing through a continuous series of intermediate 

 states. What this means is that, given any sensible 

 appearance, there will usually be, if we watch, a con- 

 tinuous series of appearances connected with the given 

 one, leading on by imperceptible gradations to the new 

 appearances which common-sense regards as those of the 

 same thing. Thus a thing may be defined as a certain 

 series of appearances, connected with each other by 

 continuity and by certain causal laws. In the case of 

 slowly changing things, this is easily seen. Consider, 

 say, a wall-paper which fades in the course of years. It 

 is an effort not to conceive of it as one " thing " whose 

 colour is slightly different at one time from what it is at 

 another. But what do we really know about it ? We 

 know that under suitable circumstances i.e. when we are, 

 as is said, " in the room " we perceive certain colours 

 in a certain pattern : not always precisely the same 

 colours, but sufficiently similar to feel familiar. If we 

 can state the laws according to which the colour varies, 

 we can state all that is empirically verifiable ; the assump- 

 tion that there is a constant entity, the wall-paper, which 

 " has " these various colours at various times, is a piece 

 of gratuitous metaphysics. We may, if we like, define 

 the wall-paper as the series of its aspects. These are 

 collected together by the same motives which led us to 

 regard the wall-paper as one thing, namely a combination 

 of sensible continuity and causal connection. More 



