THEORIES OF SCIENTIFIC CONCEPTS 159 



process." * Certain concepts of science have no direct 

 perceptual counterparts; "they are formed by an effort of 

 constructive imagination, for the purposes of the representa- 

 tive scheme . . . they must be regarded, at least provision- 

 ally, as purely ideal elements of the scheme, in fact as 

 auxiliaries necessary for the purpose of the formation of a 

 self-contained conceptual scheme which shall serve its pur- 

 pose of providing a sufficient mode of representation in 

 thought of the particular domain of physical events and 

 objects." 2 



Hobson also differs from Pearson in his conception of the 

 "representative" function of a conceptual scheme. He does 

 not believe that science merely describes, in Pearson's lim- 

 ited use of that word. The possibility of setting up a con- 

 ceptual scheme "has actual physical experience as its essen- 

 tial condition, but the constructive and generalizing work 

 of thought is no less essential. The original function of 

 such a scientific theory, or conceptual scheme, is to provide 

 an ideal representation of some more or less restricted range 

 of physical phenomena as actually observed, that is of 

 certain sequences and regularities in percepts. But the 

 functions of a conceptual scheme are much wider than those 

 of merely describing symbolically what has actually been 

 observed. The scheme is applied hypothetically to predict 

 what will be observed in circumstances which differ in some 

 degree, or in some characteristics, from those in which the 

 experiments or observations which led up to the theory 

 were made. The value and the range of validity of the partic- 

 ular conceptual scheme have to be estimated by its actual 

 success in the fulfillment of this function of prediction." 3 



Yet Hobson is not to be considered a realist. He disagrees 

 sharply with Whitehead in the latter's insistence that mole- 

 cules and electrons are natural objects. 4 'Whatever else 

 they are, molecules and electrons are concepts . . . they 

 are concepts in scientific theories, and the only question 



1 Domain of Natural Science (New York: Macmillan, 1923), p. 28. 



2 Ibid., p. 32. 3 Ibid., p. 31. 4 See above, Chapter VII, p. 133. 



