296 THE GRAMMAR OF SCIENCE 



sense-impressions, while " past history " is the conceptual 

 equivalent of the perceptual sequence in sense-impressions. 

 "Actual position" and "past history" taken in conjunction 

 thus symbolise what we have termed the routine of per- 

 ceptions (p. loi). We conclude, therefore, that if with 

 Professor Tait and other metaphysical physicists we even 

 project our conceptions into the perceptual sphere, we still 

 shall not find in " force," as either the cause of motion, or 

 the cause of change in motion, anything more than that 

 routine of perceptions which we have already seen is the 

 basis of the scientific definition of causation (p, 130). 



The idea that the past history of a corpuscle is re- 

 sumed in its present velocity is an important one. If we 

 knew the actual velocities of all existing corpuscles and 

 how their accelerations depend on relative position (or it 

 may be also on relative velocity), then theoretically, by aid 

 of the process indicated on our p. 232, or by an extension 

 of this process to extended geometrical systems, we should 

 be able to trace out the whole of the past, or, on the other 

 hand, the whole of the future history of our conceptual 

 model of the universe. The data would be sufficient to 

 theoretically solve these problems, although our brains 

 would be quite insufficient to manipulate the necessary 

 analysis. Portions of it they do, however, manage. From 

 the present velocities of earth and moon and their known 

 accelerations relative to the sun and to each other, we 

 calculate the eclipses of two or three thousand years ago, 

 and rectify our chronology by determining the dates of 

 eclipses which are recorded in the history of past human 

 experience. Or, again, from thermal or tidal data we 

 describe the condition of the universe as we conceive it to 

 have been millions of years back, or as we conceive it will 

 be millions of years hence. In all such cases we consider 

 that because our conceptual model describes very accu- 

 rately our limited perceptual experience of past and present, 

 it will continue to do so if we apply it to describe 

 sequences which cannot be verified as immediate sense- 

 impressions. In this case we are clearly making inferences, 

 but inferences which are logically justifiable (p. 60 and 



