430 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



two brain particles may be physically identical, yet they 

 may correspond to different states of mind. We are presum- 

 ably aware of this non-physical difference in brain particles 

 through introspection, though we are not informed of the 

 channels through which we become aware of such properties 

 as the "goodness" and "badness' 1 of non-brain particles. 



It follows that what is for physical science random action 

 may be for introspection caused and predictable action. 

 Given a brain particle in a certain state, physical science can 

 make no definite prediction as to its behavior, since the 

 ascertainment of both position and velocity of the particle 

 may be impossible. But introspection, being provided with 

 additional information about the particle, can anticipate its 

 behavior. Through introspection one can know whether the 

 physical state of the particle is associated with a decision of 

 one kind or with a decision of another kind; hence one can 

 predict what the behavior of the particle will be. Physics 

 must here admit its definite limitations. For, "if true free- 

 dom is postulated, with a knowledge of motives, a more 

 accurate prediction of the actions of a living being is possible 

 than can be made from a knowledge of the physical condi- 

 tions alone." x 



Two further features are required in order to complete 

 the theoretical structure. One is the volitional act itself. A 

 brain particle must be subject to control by will. Here it is 

 important to refer to Compton's figure of the mind as pro- 

 vided with a shutter by means of which it controls the orifice 

 through which the electrons pass, allowing only the "good' 

 electrons to pass and preventing the "bad'' electrons from 

 entering. Thus mind is able both to distinguish between the 

 "good" and "bad" particles, and to control their move- 

 ments. Now it is clear that such a selective and controlling 

 act will be possible provided it does not conflict with any 

 physical law. But here one need have no fears. Physical 

 science can predict only on grounds of probability, i.e., it 

 can assert that of the possible behaviors of a particle one is 



1 Ibid., p. 28. 



