THEORIES OF SCIENTIFIC CONCEPTS 153 



planation. "The law of gravitation is a brief description of 

 how every particle of matter in the universe is altering its 

 motion with reference to every other particle. It does not 

 tell us why particles thus move; it does not tell us why the 

 earth describes a certain curve around the sun. . . . Such 

 laws simply describe, they never explain the routine of our 

 perceptions." 1 Even in causal and mechanistic explanations 

 the necessity "is no categorical must, it is the descriptive 

 how of the formula, the mere summary of what has been 

 observed, the inexplicable routine." 2 "For science, cause, 

 as originating or enforcing a particular sequence of percep- 

 tions is meaningless — we have no experience of anything 

 which originates or enforces something else. Cause, how- 

 ever, used to mark a stage in a routine, is a clear and valu- 

 able conception, which throws the idea of cause entirely 

 into the field of sense-impressions, into the sphere where 

 we can reason and can reach knowledge." 3 



The function of such concepts in science is therefore not 

 to explain but to describe. "Atom and molecule are intel- 

 lectual conceptions by the aid of which physicists classify 

 phenomena and formulate the relationships of their se- 

 quences." 4 "The fundamental conceptions of geometry 

 are only ideal symbols which enable us to form an approx- 

 imate, but in no sense absolute, analysis of our sense- 

 impressions. They are the scientific shorthand by which 

 we describe, classify, and formulate the characteristics of 

 that mode of perception which we term perceptual space." 5 

 It seems safe to say that by such concepts as these we mean 

 simply the sense-impressions which they serve to classify. 

 Hence the imaginative operations which call such symbols 

 into being prove to be nothing more than techniques of 

 classification. 



It follows that we must not ascribe to symbols which are 

 merely simplifying devices any phenomenal existence other 

 than that of the sense-impressions which they classify. ' To 



1 Ibid., p. 99. 3 Ibid., pp. 128-129. 5 Ibid., pp. 198-199. 



2 Ibid., pp. 126-127. 4 Ibid., p. 95. 



