156 THE GRAMMAR OF SCIENCE 



of sense-impressions and their order space. A single 

 sense-impression might, indeed, exist for us without any 

 coexisting groups being postulated, but space would have 

 no meaning if there were not such coexisting groups. 

 Space is an order or mode of perceiving objects, but it 

 has no existence if objects are withdrawn, no more than 

 the alphabet could have an existence if there were no letters. 

 If the reader has once grasped this point — and it is 

 undoubtedly a difficult and hard one (for our senses of 

 sight and touch lead us imperceptibly to confuse the 

 reality of sense-impressions with our mode of perceiving 

 them), — then he will cease to look upon space as an 

 enormous void in which objects have been placed by an 

 agency in nowise conditioned by his own perceptive 

 faculty ; he will begin to consider space as an order of 

 things, but not itself a thing. To say, therefore, that 

 a thing " exists in space " is to assert that the per- 

 ceptive faculty has distinguished it as a group of 

 sense-impressions from other groups of sense-impressions, 

 which actually or possibly coexist. We cannot dog- 

 matically deny that the order of coexisting phenomena 

 " arises " from something behind sense-impressions,^ but 

 we may feel pretty confident that space, our mode of 

 perceiving these phenomena, is very different from any- 

 thing in the unknowable world behind sense-impressions. 

 Once recognise space as a mode of the perceptive faculty, 

 and it appears as something peculiar to the individual 

 perceptive faculty. Without any perceptive faculty it is 

 conceivable that sensations might exist (see p. 102), but 

 there could not be that mode of perception we term 

 space. The remarkable fact is this : that the order of 

 coexisting phenomena is apparently the same at any rate 

 for the vast majority of human perceptive faculties. Why 

 should this mode of perception be the same for all normal 

 human faculties — or, perhaps it would be better to say, 



1 Just as little ought we to assert that it does. The word ai-ise suggests 

 causation : but the word causation is meaningless as a relation between the 

 unknowable beyond of sense-impression and sense-impression itself (see pp. 

 68 and 127) 



