The Law of Demand 81 



that has a bearing upon the a priori theory of demand. 

 In treatises on pure economics, particularly in those in 

 which mathematical analysis is employed, the masters 

 of the a priori method point out what they regard as 

 the extreme difficulty of the actual problem of the rela- 

 tion of price to quantity of commodity — a difficulty 

 growing out of the interrelation of the many factors in 

 the problem. If, to limit the illustration to a simple 

 case, one wishes to know how the price of corn is re- 

 lated to the quantity of corn that is produced, he is 

 told that the problem is inextricably complex: If there 

 is a deficiency in corn, then hay, or potatoes, or oats, 

 or all three may be substituted in part for corn, and con- 

 sequently the variation in the price of corn that fol- 

 lows upon a deficiency of corn cannot be traced with- 

 out knowing in what degree, when the price of corn 

 varies, hay, oats, and potatoes are used as substitutes. 

 But this is not all. The degree in which hay, oats, and 

 potatoes are substituted for corn is dependent not only 

 upon the price of corn but also on their own several 

 prices, and these latter prices are, in turn, dependent 

 upon the supply and price of corn ! This statement of 

 the problem, complex as it appears, is unduly simpli- 

 fied; and it is presented not in order to ridicule the work 

 of the masters who have elaborated the method of 

 stating the problem in the form of simultaneous equa- 

 tions, but to show how hopelessly remote from reality 

 is the very best theoretical treatment of the problem 

 of the relation of price to the quantity of commodity, 

 and to suggest, from the results of the preceding pages 



