SENSE-DATA AND PHYSICS 147 



data. We have therefore to solve the equations giving 

 sense-data in terms of physical objects, so as to make 

 them instead give physical objects in terms of sense- 

 data. 



II. CHARACTERISTICS OF SENSE-DATA 



When I speak of a " sense-datum," I do not mean the 

 whole of what is given in sense at one time. I mean 

 rather such a part of the whole as might be singled out 

 by attention : particular patches of colour, particular 

 noises, and so on. There is some difficulty in deciding 

 what is to be considered one sense-datum : often atten- 

 tion causes divisions to appear where, so far as can be 

 discovered, there were no divisions before. An observed 

 complex fact, such as that this patch of red is to the left 

 of that patch of blue, is also to be regarded as a datum 

 from our present point of view : epistemologically, it 

 does not differ greatly from a simple sense-datum as 

 regards its function in giving knowledge. Its logical 

 structure is very different, however, from that of sense : 

 sense gives acquaintance with particulars, and is thus a 

 two-term relation in which the object can be named but 

 not asserted, and is inherently incapable of truth or false- 

 hood, whereas the observation of a complex fact, which 

 may be suitably called perception, is not a two-term 

 relation, but involves the prepositional form on the 

 object-side, and gives knowledge of a truth, not mere 

 acquaintance with a particular. This logical difference, 

 important as it is, is not very relevant to our present 

 problem ; and it will be convenient to regard data of 

 perception as included among sense-data for the purposes 

 of this paper. It is to be observed that the particulars 

 which are constituents of a datum of perception are 

 always sense-data in the strict sense. 



