SENSE-DATA AND PHYSICS 175 



only acquire meaning when put into a context which, 

 with them, forms a proposition. Thus such pairs of words 

 can be appHed to descriptions, ^ but not to proper names : 

 in other words, they have no appUcation whatever to 

 data, but only to entities or non-entities described in 

 terms of data. 



Let us illustrate by the terms " existence " and " non- 

 existence." Given any datum x, it is meaningless either 

 to assert or to deny that x *' exists." We might be 

 tempted to say : ''Of course x exists, for otherwise it 

 could not be a datum." But such a statement is really 

 meaningless, although it is significant and true to say 

 " My present sense-datum exists," and it may also be 

 true that " a; is my present sense-datum." The inference 

 from these two propositions to " x exists " is one which 

 seems irresistible to people unaccustomed to logic ; yet 

 the apparent proposition inferred is not merely false, but 

 strictly meaningless. To say " My present sense-datum 

 exists " is to say (roughly) : " There is an object of which 

 ' my present sense-datum ' is a description." But we 

 cannot say : *' There is an object of which * x' is a 

 description," because ' i\; ' is (in the case we are supposing) 

 a name, not a description. Dr. Whitehead and I have 

 explained this point fully elsewhere (loc. cit.) with the 

 help of symbols, without which it is hard to understand ; 

 I shall not therefore here repeat the demonstration of the 

 above propositions, but shall proceed with their applica- 

 tion to our present problem. 



The fact that " existence " is only applicable to 

 descriptions is concealed by the use of what are gram- 

 matically proper names in a way which really transforms 

 them into descriptions. It is, for example, a legitimate 



^ Cf. Principia Mathematica, Vol. I, * 14, and Introduction, Chap. 



