70 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



its relations are more or less arbitrarily neglected, and are 

 not included in the resulting symbol. As a consequence, 

 every symbol is abstract in its representation of nature; it 

 loses some of nature, and hence is not strictly adequate as a 

 representative. Thus the realm of symbols is less extensive 

 than the realm of events. But, in the second place, the 

 human mind seems to be unwillingly restrained to what is 

 given; it is prone to soar into flights of imagination and 

 theorizing, which go beyond the limits of the obvious data 

 and result in the formation of symbols having no known 

 existential correlates. These methods may be purely imagina- 

 tive, and guided by no recognized techniques, as in the case 

 of poetry and much common sense reflection; or they may be 

 subject to greater or less control, as in the case of science. 

 But even in the latter case a greater variation in methods is 

 possible. The operations by which the realm of the given is 

 extended may be essentially Active and creative, resulting in 

 such entities as perfect levers, ideal gases, disembodied 

 electrical charges, and mathematical points. Or they may 

 be more closely tied down to the realm of the given in the 

 sense that they are possible constructions out of it ; a physical 

 object, for example, may be defined as the class of its ap- 

 pearances, 1 a mathematical point may be defined as the 

 series of "enclosing' events, 2 space may be defined as the 

 totality of possibilities of relative position of bodies and 

 phenomena. 3 Finally, the operations may be considered as 

 semi-exploratory in character, and hence as resulting in 

 entities which have at least a probable existence; such 

 techniques produce what are ordinarily called hypotheses. 

 What is important with reference to all of these entities 

 is that they are not, at least at the moment of creation, 

 considered as indubitably given. As a consequence one is 

 obliged, by virtue of a characteristic activity of the mind, 



1 Bertrand Russell, Our Knowledge of the External World (Chicago: Open Court, 

 1915), p. 155. 



2 A. N. Whitehead, Concept of Nature (Cambridge: Cambridge University Press, 

 1920), Chap. IV. 



3 V. F. Lenzen, Physical Theory (New York: Wiley, 1931), p. 51. 



