142 MYSTICISM AND LOGIC 



perspective to another that defines the class of particulars 

 which is to be called " one thing." 



Broadly speaking, we may say that the physicist finds 

 it convenient to classify particulars into " things," while 

 the psychologist finds it convenient to classify them into 

 ' perspectives " and " biographies," since one perspective 

 may constitute the momentary data of one percipient, and 

 one biography may constitute the whole of the data of 

 one percipient throughout his life. 



We may now sum up our discussion. Our object has 

 been to discover as far as possible the nature of the 

 ultimate constituents of the physical world. When I 

 speak of the ' physical world," I mean, to begin with, 

 the world dealt with by physics. It is obvious that 

 physics is an empirical science, giving us a certain amount 

 of knowledge and based upon evidence obtained through 

 the senses. But partly through the development of 

 physics itself, party through arguments derived from 

 physiology, psychology or metaphysics, it has come to 

 be thought that the immediate data of sense could not 

 themselves form part of the ultimate constituents of the 

 physical world, but were in some sense " mental," " in 

 the mind," or " subjective." The grounds for this view, 

 in so far as they depend upon physics, can only be ade- 

 quately dealt with by rather elaborate constructions 

 depending upon symbolic logic, showing that out of such 

 materials as are provided by the senses it is possible to 

 construct classes and series having the properties which 

 physics assigns to matter. Since this argument is diffi- 

 cult and technical, I have not embarked upon it in this 

 article. But in so far as the view that sense-data are 

 ' mental ' ' rests upon physiology, psychology, or meta- 

 physics, I have tried to show that it rests upon con- 

 fusions and prejudices prejudices in favour of per- 

 manence in the ultimate constituents of matter, and 



