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 ordecision as observed in producing, consuming and exchanging goodsand services.

To fix the idea of utility the economist should go no farther thanis serviceable in explaining economic facts. It is not his province tobuild a theory of psychology. It is not necessary for him to takesides with those who wrangle to prove or disprove that pleasure andpain alone determine conduct. These disputants have so mangledthe ideas of pleasure and pain that he who follows them and theircircular arguments finds himself using the words in forced senses.

Jevons makes utility synonymous with pleasure. Cairnes* objectsand claims that it leads to a circular definition of value. The circleis however at the very beginning and vitiates psychology not eco-nomics; the last dollar’s worth of sugar (we are told) represents thesame quantity of pleasurable feeling as the last dollar’s worth ofdentistry. This may be true as a mere empty definition, but wemust beware of stating it, as a real “ synthetic proposition,”! or ofconnecting it with the mathematics of sensationsj 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 thedistinction between pleasure and desire. || No one ever denied thateconomic acts have the invariable antecedent, desire. Whether thenecessary antecedent of desire is “ pleasure ” or whether indepen-dently of pleasure it may sometimes be “ duty ” or “ fear ” concernsa phenomenon in the second remove from the economic act of choiceand 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. 21. f Kant , Critique Pure Reason, Introduction.

t Ladd, Physiological Psychology, p. 361. § See above (Preface).

( See Sidgwiek, Methods of Ethics, Chap. IV.