152 MYSTICISM AND LOGIC 



Logically a sense-datum is an object, a particular of 

 which the subject is aware. It does not contain the 

 subject as a part, as for example beliefs and volitions do. 

 The existence of the sense-datum is therefore not logically 

 dependent upon that of the subject ; for the only way, 

 so far as I know, in which the existence of A can be 

 logically dependent upon the existence of B is when B 

 is part of A. There is therefore no a priori reason why a 

 particular which is a sense-datum should not persist 

 after it has ceased to be a datum, nor why other similar 

 particulars should not exist without ever being data. 

 The view that sense-data are mental is derived, no doubt, 

 in part from their physiological subjectivity, but in part 

 also from a failure to distinguish between sense-data and 

 &quot; sensations.&quot; By a sensation I mean the fact consisting 

 in the subject s awareness of the sense-datum. Thus a 

 sensation is a complex of which the subject is a con 

 stituent and which therefore is mental. The sense-datum, 

 on the other hand, stands over against the subject as that 

 external object of which in sensation the subject is 

 aware. It is true that the sense-datum is in many cases 

 in the subject s body, but the subject s body is as dis 

 tinct from the subject as tables and chairs are, and is in 

 fact merely a part of the material world. So soon, there 

 fore, as sense-data are clearly distinguished from sensa 

 tions, and as their subjectivity is recognised to be physio 

 logical not psychical, the chief obstacles in the way of 

 regarding them as physical are removed. 



V. &quot; SENSIBILIA &quot; AND 



But if &quot; sensibilia &quot; are to be recognised as the ultimate 

 constituents of the physical world, a long and difficult 

 journey is to be performed before we can arrive either at 



