84 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



Positivism insists that the fundamental error in the com- 

 mon sense interpretation lies in the supposition that all 

 that any observer knows is ideas, private to his own mind. 

 One knows neither ideas nor objects, says positivism, but 

 neutral entities which are in themselves neither mental nor 

 physical. According to Ernst Mach, one of the most sig- 

 nificant representatives of the position, the stuff of knowledge 

 consists of such neutral entities — "colors, sounds, tem- 

 peratures, pressures, spaces, times, . . . feelings and voli- 

 tions." * These elements are not psychical in character, nor 

 private to the mind of the observer. Nor are they physical, 

 residing in a public world. Strictly speaking, they are in 

 themselves neither the one nor the other. However, they 

 have the capacity to occur in certain types of complexes 

 and in certain functional relationships to one another. "A 

 color is a physical object as soon as we consider its depend- 

 ence, for instance, upon its luminous source, upon other 

 colors, upon temperature, upon spaces, and so forth. When 

 we consider, however, its dependence upon the retina it is a 

 psychological object, a sensation. Not the subject-matter 

 but the direction of our investigation, is different in the 

 two domains." 2 "These elements — elements in the sense 

 that no further resolution has as yet been made of them — 

 are the simplest materials out of which the physical, and 

 also the psychological, world is built up." 3 Hence knowl- 

 edge cannot be an affair involving correspondence between 

 a psychical entity and a physical entity, for there is no such 

 difference of stuff. An element in one context is psychical, 

 and in another is physical; but it is the same element in 

 both cases. 



Such a theory claims to avoid the unfortunate dualism 

 of common sense. When a color is known, there is not the 

 idea of the color which is known directly, and the physical 

 color itself which is outside of the mind and known only 

 indirectly. The color and the idea of the color are identical. 



1 Analysis of Sensations (Chicago: Open Court, 1914), p. 2. 



2 Ibid., p. 17. 3 Ibid., p. 42. 



