No. 558] CAUSES AND DETERMINERS 



359 



jected to the same conditions of light, an internal dif- 

 ference of condition may not equally unequivocally de- 

 termine a difference in the movement (so that one may, 

 for example, move toward the source of light while the 

 other does not), it is incorrect. What is unequivocally 

 determined is always a difference between two cases; 

 what determines the difference depends on the compari- 

 son made. 



F. Some assert that physical conditions affect psychic 

 states, and vice versa; that the physical and psychical 

 interact; others dissent. 



To assert that physical conditions affect psychic states 

 can mean only, from a radically experimental point of 

 view, that a preceding alteration in an exclusively phys- 

 ical condition results in a change in a psychical condi- 

 tion (pain, sensation). The experiment appears to occur 

 frequently, and to give as unequivocal results as any ex- 

 periments in science (unless we suspect all physical 

 changes to be accompanied by psychical ones, in which 

 case we drop the radically experimental standpoint). 

 (It will be observed that experimentation can have noth- 

 ing to say on the question sometimes discussed as to 

 whether the physical and psychic conditions occurring 

 at the same time have a relation of cause and effect; this 

 is a typical example of a question that can not be re- 

 duced to an experimental situation.) 



The converse assertion is that a change in an exclu- 

 sively psychical condition produces a change in physical 

 conditions. The experimental situation is not a conceiv- 

 able one, unless psychical changes do occur unaccom- 

 panied by physical ones. 



G. Some assert that entelechy is required for deter- 

 mining what happens in development; others dissent. 



The bearing that experiment can have on this question 

 is to discover whether there ever occur cases in which 

 two systems alike in all perceptual respects act in two 

 perceptually different ways. If no such cases occur, no 

 additional agent is experimentally demanded. If such 



