FIRST APPROXIMATION

rigidly prescribed income stream to the hypothesis of anincome stream which, while it may be decreased at will,cannot be increased beyond a fixed amount at eachperiod of time. While free to decrease his income in anyperiod, its possessor would not do so unless thereby hecould secure an increase in some other period.

Not only is such an hypothesis quite thinkable, it isprobably actually approximated in primitive communi-ties. In our own day most men have opportunities (quiteapart from lending to others at interest) to secure muchreal income in future years by temporarily sacrificing alittle immediate real income as, for instance, by invest-ing labor in building a house or machine. But we canreadily suppose a situation such that this year’s produc-tion and next year’s production would be almost inde-pendent of each other. This situation is true of most ani-mals and even of man in the hunting and fishing stage,and before that stage even more markedly when his onlyimplements were his hands. And even in our own civili-zation, many are mere stipendiaries, virtually withoutany opportunity to add to future income except bylending at interest.

The essence of the hypothesis therefore on which thefirst approximation rests is that we are not to be both-ered by the possibility of a man’s thus increasing his in-come in one period through decreasing it in another ex-cept through the process of trading some of one year’sincome with another person for some of another year’sincome.

We may in fact for practical purposes picture the in-come stream of each person as thus fixed for only afew years, and assume that expectation of income beyondthose years so indefinite as to have no effect on the

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