EXAMINATION OF THE PRINCIPLES 153 



tions in allied sciences all these are tending so to transform our 

 ideas of the functions performed by the 'economic man,' that 

 the classical description of him is no longer appropriate. 



What we find to be true of this principle of economics applies 

 in some measure, we believe, to all general laws. The validity 

 of a universal principle is not a matter of its own individual 

 adequacy as a description of reality; nor, again, is its validity 

 elative to the whole existing body of human knowledge (if, 

 indeed, we can speak of such a thing). It may correctly enough 

 be said that the validity of such a principle depends upon its 

 place in the developing structure of our knowledge, if we remem- 

 ber that this place is not definitely determined, but is exceed'ngly 

 variable. A law is not judged as true because it marks the limit 

 of human knowledge and because we are not able to correct 

 any given formulation of it. Its truth is always a matter of 

 context. It is valid if we find a certain harmony between the 

 character and degree of its abstractness and the character and 

 definiteness of the conclusions in view of which it is asserted. 



A process of reasoning can proceed only by assuming a set of 

 premises, partly explicit and partly implicit, as valid for the 

 purposes of the argument in hand. Without such fixed point of 

 departure, no coherent reasoning would be possible. The hypo- 

 thetically valid premise is a fulcrum by means of which we move 

 the unwie'dy masses of fact and theory with which our thought 

 is to cope. But to make an assumption with regard to any con- 

 crete subject is to make an abstraction; it is to single out certain 

 characteristics, and to regard these out of connection with others 

 which are equally constitutive of the subject in other relations. 

 What is thus singled out and regarded as the nature of the subject 

 is what is relevant to our purpose in thinking of the subject at all. 

 And what is disregarded as negligible is what is irrelevant and 

 foreign to our interest. Hence it happens that for the purposes 

 of some other argument it may be possible and even necessary 

 to assume other and often contradictory propositions concerning 

 the same subject, which are then regarded as valid, while the 



