THE LOGICAL STRUCTURE OF SCIENCE 51 



taining conflicting claims with reference to its descriptive 

 values. One must, therefore, consider this element of cogni- 

 tion in greater detail. 



The important feature of knowledge seems to be that 

 when one knows the realm of events he is aware of it in dif- 

 ferent ways, and knowledge itself is a composite of these 

 different kinds of awareness. A convenient approach to this 

 problem is through a distinction suggested by Russell be- 

 tween "knowledge by acquaintance' and "knowledge by 

 description." "We shall say that we have acquaintance with 

 anything of which we are directly aware, without the inter- 

 mediary of any process of inference or any knowledge of 

 truths. Thus in the presence of my table I am acquainted 

 with the sense-data that make up the appearance of my 

 table — its color, shape, hardness, smoothness, etc.; all these 

 are things of which I am immediately conscious when I 

 am seeing and touching my table. . . . My knowledge of 

 the table as a physical object, on the contrary, is not direct 

 knowledge. Such as it is, it is obtained through acquaintance 

 with the sense-data that make up the appearance of the 

 table. . . . My knowledge of the table is of the kind which 

 we shall call 'knowledge by description.' The table is 'the 

 physical object which causes such-and-such sense-data.' . . . 

 All our knowledge of the table is really knowledge of truths, 

 and the actual thing which is the table is not, strictly speak- 

 ing, known to us at all." * Elsewhere he speaks of descrip- 

 tive knowledge as knowledge expressible in the form "a so- 

 and-so' and "the so-and-so," and he suggests that when 

 we know descriptively through propositions, 'it is only 

 what we may call the concept that enters into the proposi- 

 tion." 2 "Common words, even proper names, are usually 

 really descriptions." 3 



1 Bertrand Russell, Problems of Philosophy (New York: Henry Holt, 1912), 

 pp. 73-75. 



2 Bertrand Russell, Introduction to Mathematical Philosophy (London: Allen and 

 Unwin, 1920), p. 168. 



3 Bertrand Russell, Mysticism and Logic (London: Longmans, Green, 1921), 

 p. 216. For another formulation of the distinction see A. N. Whitehead, Symbolism, 

 Its Meaning and Effect (New York: Macmillan, 1927), pp. 7 el seq. 



