SPACE AND TIME 155 



permanently grouped together, and, in the second place, 

 from the mental habit of concentrating our attention on 

 one of these groups by placing about it in conception an 

 arbitrary boundary separating it from other groups. Such 

 arbitrary boundaries are conceptions drawn doubtless from 

 sense-impressions of sight and touch, but they correspond, 

 as we shall soon see, to nothing real in the world of sense- 

 impression or in phenomena. 



The coexistence of more or less permanent and distinct 

 groups of sense-impressions is a fundamental mode of 

 our perception ; it is one of the ways in which we per- 

 ceive things apart. There is nothing in sense-impressions 

 themselves which involves the notion of space, but 

 whether space be " due " to something behind sense- 

 impression or to the nature of the perceptive faculty itself 

 we are unable at present to decide. Leibniz has defined 

 space as the order of possible coexisting phenomena. 

 This order may " arise " from something behind pheno- 

 mena, or from the machinery of perception, but in either 

 case the order itself is simply a mode or manner in which 

 we perceive things. The reader must distinguish carefully 

 between the groups of sense-impressions themselves and 

 the order in which we perceive them to coexist. Per- 

 haps the distinction will be best brought out by con- 

 sidering the letters of the alphabet : — 



A, B, C, D, E, F, G, . . . 



The letters may be said to have a real existence like the 

 groups of sense-impressions we term objects. The order 

 of the letters is merely the mode in which we perceive 

 them to coexist as an alphabet. The " existence " we 

 attribute to the order is thus of a totally different 

 character from the " existence " we attribute to the letters. 

 The alphabet has in itself no existence except for the 

 letters it contains, but the letters, on the other hand, could 

 have a real existence if they had never been arranged 

 in any order or alphabet. The alphabet has merely 

 existence as a manner of looking at all the letters together. 

 These results may all be interpreted of coexisting groups 



