154 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



no concept, however invaluable it may be as a means of describ- 

 ing the routine of perceptions, ought phenomenal existence to 

 be ascribed until its perceptual equivalent has been actually 

 disclosed" 1 'Science takes the universe of perceptions as 

 it finds it, and endeavors briefly to describe it. It asserts 

 no perceptual reality for its own shorthand." 2 



Such a position is definitely positivistic. It defines clearly 

 the realm about which the scientist is permitted to talk — 

 the realm of sense-impressions. These alone can be said to 

 be given clearly. The task of science with reference to these 

 entities is that of mere classification, ordering, and cor- 

 relating. Any symbols which presume to refer to entities 

 not directly observable must be recognized for what they 

 are, viz., merely devices for classification, ordering, and 

 correlating. Science does not explain, but describes. 



OPERATIONALISM 



A somewhat more recent form of positivism is that of 

 P. W. Bridgman. This physicist's starting-point is the 

 recognition of two facts: the presence of discontinuities in 

 the realm of experience, and the necessity for a pure empiri- 

 cism. "The first lesson of our recent experience with rela- 

 tivity is merely an intensification and emphasis of the les- 

 son which all past experience has also taught, namely, 

 that when experiment is pushed into new domains, we must 

 be prepared for new facts, of an entirely different character 

 from those of our former experience." 3 We must not be 

 surprised, therefore, if we find that the concepts defined in 

 terms of the " middle-sized' objects of ordinary experience 

 fail of application, or become meaningless when extended 

 to the range of cosmic phenomena on the one hand, or to 

 microscopic phenomena on the other. "As we approach 

 the experimentally attainable limit, concepts lose their indi- 

 viduality, fuse together, and become fewer in number." 4 

 Heat, for example, does not apply to molecules, nor do space 



1 Ibid., p. 277 (italics are the author's). 2 Ibid., p. 208. 



3 Logic of Modern Physics (New York: Macmillan, 1927), p. 2. * Ibid., p. 24. 



