The Law of Demand 67 



explanation of the phenomenon is to investigate in 

 turn, theoretically, the effect upon price of each factor, 

 coeteris -paribus, and then finally to make a synthesis! 

 But if in case of the relation of each factor to price the 

 assumption cceteris paribus involves large and at least 

 questionable hypotheses, does one not completely lose 

 himself in a maze of implicit hypotheses when he speaks 

 of a final synthesis of the several effects? We shall not 

 adopt this bewildering method, but shall follow the 

 opposite course and attack the problem of the relation 

 of prices and supply in its full concreteness. 



The fruitfulness of the statistical theory of correlation 

 stands in significant contrast to the vast barrenness of 

 the method that has just been described, and the two 

 methods follow opposed courses in dealing with a 

 problem of multiple effects. Take, for example, the 

 question of the effects of weather upon crops. What a 

 useless bit of speculation it would be to try to solve, in a 

 hypothetical way, the question as to the effect of rain- 

 fall upon the crops, other unenumerated elements of 

 weather remaining constant? The question as to the 

 effect of temperature, cceteris paribus? How, finally, 

 would a synthesis be made of the several individual 

 effects? The statistical method of multiple correlation 

 formulates no such vain questions. It inquires, di- 

 rectly, what is the relation between crop and rainfall, 

 not c&teris paribus, but other things changing accord- 

 ing to their natural order; what is the relation between 

 crop and temperature, other things conforming to the 

 observed changes in temperature; and, finally, what is 



