SENSE-DATA AND PHYSICS 157 



physics, where, I do not doubt, it would have been apphed 

 long ago but for the fact that all who have studied this 

 subject hitherto have been completely ignorant of mathe- 

 matical logic. I myself cannot claim originality in the 

 application of this method to physics, since I owe the 

 suggestion and the stimulus for its application entirely 

 to my friend and collaborator Dr. Whitehead, who is 

 engaged in applying it to the more mathematical portions 

 of the region intermediate between sense-data and the 

 points, instants and particles of physics. 

 rr A complete application of the method which substitutes 

 1 1 constructions for inferences would exhibit matter wholly 

 I in terms of sense-data, and even, we may add, of the sense- 

 data of a single person, since the sense-data of others 

 cannot be known without some element of inference. 

 This, however, must remain for the present an ideal, to 

 be approached as nearly as possible, but to be reached, if 

 at all, only after a long preliminary labour of which as 

 yet we can only see the very beginning. The inferences 

 which are unavoidable can, however, be subjected to 

 certain guiding principles. In the first place they should 

 always be made perfectly explicit, and should be formulated 

 in the most general manner possible. In the second place 

 the inferred entities should, whenever this can be done, be 

 similar to those whose existence is given, rather than, like 

 the Kantian Ding an sich, something wholly remote from 

 the data which nominally support the inference. The 

 inferred entities which I shall allow myself are of two 

 kinds : (a) the sense-data of other people, in favour of 

 which there is the evidence of testimony, resting ulti- 

 mately upon the analogical argument in favour of minds 

 other than my own ; (b) the " sensibilia " which would 

 appear from places where there happen to be no minds, 

 and which I suppose to be real although they are no one's 



