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 w^ere 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 propositional 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. 



