WORLDS OF PHYSICS AND OF SENSE 107 



generally, a " thing " will be defined as a certain series 

 of aspects, namely those which would commonly be said 

 to be of the thing. To say that a certain aspect is an 

 aspect of a. certain thing will merely mean that it is one 

 of those which, taken serially, are the thing. Everything 

 will then proceed as before : whatever was verifiable is 

 unchanged, but our language is so interpreted as to avoid 

 an unnecessary metaphysical assumption of permanence. 



The above extrusion of permanent things affords an 

 example of the maxim which inspires all scientific philo- 

 sophising, namely "Occam's razor": Entities are not to 

 be multiplied without necessity. In other words, in dealing 

 with any subject-matter, find out what entities are 

 undeniably involved, and state everything in terms of 

 these entities. Very often the resulting statement is 

 more complicated and difficult than one which, like 

 common sense and most philosophy, assumes hypothetical 

 entities whose existence there is no good reason to believe 

 in. We find it easier to imagine a wall-paper with 

 changing colours than to think merely of the series of 

 colours ; but it is a mistake to suppose that what is easy 

 and natural in thought is what is most free from un- 

 warrantable assumptions, as the case of " things ' very 

 aptly illustrates. 



The above summary account of the genesis of " things," 

 though it may be correct in outline, has omitted some 

 serious difficulties which it is necessary briefly to consider. 

 Starting from a world of helter-skelter sense-data, we 

 wish to collect them into series, each of which can be 

 regarded as consisting of the successive appearances of 

 one " thing." There is, to begin with, some conflict 

 between what common sense regards as one thing, and 

 what physics regards an unchanging collection of particles. 

 To common sense, a human body is one thing, but to 



