SPACE AND TIME 167 



scientific conceptions does not in the first place depend on 

 their reality as perceptions, but on the means they provide 

 of classifying and describing perceptions. If a circle and 

 a rectangle have no real existence, they are still invaluable 

 as enabling me to classify my perceptions of form, to 

 describe, however imperfectly, the difference in shape 

 between the faces of a page of this book and of my 

 watch. They are symbols in that shorthand by means 

 of which science describes the universe of phenomena. 

 The atom, if a pure conception, still enables us, by 

 codifying our past experience, to economise thought ; it 

 preserves within reasonable limits the material upon which 

 we base our prediction of possible future experience. If 

 any one tells us that the storm-god is to some minds as 

 conceivable as the atom, we must, in the first place, 

 reply that the conceivable is not the real ; and further, 

 that the value to man of any ideal of conception depends 

 upon the extent to which it subsumes the future in its 

 resume of the past. The conception storm-god may, after 

 all, be of some value as a striking monument to our 

 meteorological ignorance, and as a useful reminder that 

 we must " be prepared for all weathers." 



What we have at this stage to notice is that the mind 

 is not limited to perceptual association, and that it can 

 carry on in conception a process which may be begun 

 but cannot be indefinitely continued in the sphere of 

 perception. The scientific value of such conceptions, 

 whether reached by association or as a limit, must in 

 every case be judged by the extent to which they enable 

 us to classify, describe, and predict phenomena. 



% 6. — Saincjicss and CoiitinuAty 



Now there are two ideas reached as conceptual limits 

 ' to perceptual processes which have important bearings on 

 the geometrical representation of space. These may be 

 expressed by the words sameness and continuity. So far 

 as our perceptual experience goes, probably no two groups 

 of sense-impressions are exactly the same. The sameness 



