CONSTITUENTS OF MATTER 139 



between the different parts of the sensible space perceived 

 by one man, do not hold between parts of sensible spaces 

 perceived by different men. There are therefore a multi- 

 tude of three-dimensional spaces in the world : there are 

 all those perceived by observers, and presumably also 

 those which are not perceived, merely because no observer 

 is suitably situated for perceiving them. 



But although these spaces do not have to one another 

 the same kind of spatial relations as obtain between the 

 parts of one of them, it is nevertheless possible to arrange 

 these spaces themselves in a three-dimensional order 

 This is done by means of the correlated particulars which 

 we regard as members (or aspects) of one physical thing. 

 When a number of people are said to see the same object, 

 those who would be said to be near to the object see a 

 particular occupying a larger part of their field of vision 

 than is occupied by the corresponding particular seen by 

 people who would be said to be farther from the thing. 

 By means of such considerations it is possible, in ways 

 which need not now be further specified, to arrange all 

 the different spaces in a three-dimensional series. Since 

 each of the spaces is itself three-dimensional, the whole 

 world of particulars is thus arranged in a six-dimensional 

 space, that is to say, six co-ordinates will be required to 

 assign completely the position of any given particular, 

 namely, three to assign its position in its own space and 

 three more to assign the position of its space among the 

 other spaces. 



There are two ways of classifying particulars : we may 

 take together all those that belong to a given " perspec- 

 tive," or all those that are, as common sense would say, 

 different " aspects " of the same " thing." For example, 

 if I am (as is said) seeing the sun, what I see belongs to 

 two assemblages : (i) the assemblage of all my present 

 objects of sense, which is what I calJ a " perspective " ; 



