126 TIME 



of our domain — so time marks the progression of perceptions 

 to a position in space. The combination of these two modes 

 or change of position with change of time is motion, which is 

 the basic condition of our perception. 



At first glance it seems, however, that there are certain 

 fundamental differences between space and time. For 

 instance, space, taken as a method of perceiving coexisting 

 objects, according to the idea developed amongst others by 

 Karl Pearson^ and as a mode of perception enabling us to 

 distinguish groups of immediate sense-impressions, is asso- 

 ciated with the world of actual phenomena which we project 

 beyond us. For this reason it has been called a mode of 

 external perception. 



On the other hand, time is the perception of sequence in 

 the accumulated sense-impressions. It is the relation between 

 past perceptions and present perceptions. Thus, time in its 

 essence, impHes memory and thought, or in other words: 

 consciousness. In reality consciousness could be defined as 

 the power to perceive things separately in succession. From 

 this standpoint, time has been called an internal mode of 

 perception. This is in substance Bergson's idea of duration 

 which we will take up again later. A moment's reflection 

 soon shows, however, that this differentiation has no value, for 

 no distinction based on the words 'external' or 'internal' can 

 exist. Indeed, the perceptions of exterior objects can always 

 be traced back to the simple sense-impressions through which 

 we know these objects. It is therefore clear that the arbitrary 

 difference between the exterior and the interior of our ego is 

 nothing but a simple distinction of daily practical convention. 



'Take a needle,' says Pearson. 'We say that it is thin, 

 bright, pointed and so forth. What are these properties 

 but a group of sense-impressions relating to form and 

 colour associated with conceptions drawn from past sense- 

 impressions? Their immediate source is the activity of 

 certain optic nerves. These sense-impressions form for us 

 ^ Pearsorij Karl, The Grammar of Scietice, 3rd ed., 1911, London. 



