Part I. — Utility of each commodity assumed to be depen- 

 dent ONLY ON the quantity OF THAT COMMODITY. 



CHAPTER I. 



UTILITY AS A QUANTITY. 



§1. 



The laws of economics are framed to explain facts. The concep- 

 tion of utility has its origin in the facts of human preference or 

 decision as observed in producing, consuming and exchanging goods 

 and services. 



To fix the idea of utility the economist should go no farther than 

 is serviceable in explaining economic facts. It is not his province to 

 build a theory of psj^chology. It is not necessary for him to take 

 sides with those who wrangle to prove or disprove that pleasure and 

 pain alone determine conduct. These disputants have so mangled 

 the ideas of pleasure and pain that he who follows them and their 

 circular arguments finds himself using the words in forced senses. 



Jevons makes utility synonymous with pleasure. Cairnes* objects 

 and claims that it leads to a circular definition of value. The circle 

 is however at the very beginning and vitiates psychology not eco- 

 nomics; the last dollar's worth of sugar (we are told) represents the 

 same quantity of pleasurable feeling as the last dollar's worth of 

 dentistry. This may be true as a mere empty definition, but we 

 must beware of stating it, as a real " synthetic proposition, "f or of 

 connecting it with the mathematics of sensations^ as did Edgeworth.§ 



The plane of contact between psychology and economics is desire. 

 It is difficult to see why so many theorists endeavor to obliterate the 

 distinction between j)leasure and desire. || No one ever denied that 

 economic acts have the invariable antecedent, desire. Whether the 

 necessary antecedent of desire is " pleasure " or whether indepen- 

 dently of pleasure it may sometimes be " duty " or " fear " concerns 

 a. phenomenon in the second remove from the economic act of choice 

 and is completely within the realm of psychology. 



We content ourselves therefore with the following simple psycho- 

 economic postulate: 



Each individual acts as he desires. 



* Pol. Econ., p. 31. f Kant, Critique Pure Reason, Introduction. 



X Ladd, Physiological Psychology, p. 361. i^ See above (Preface). 



II See Sidgwick, Methods of Ethics, Chap. IV. 



