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 little reluctance to part with if in so doing one can obtain something wanted; on the other hand, if the getting of a pair of shoes calls for the giving up of a month's labor, an inhibitory influence comes into play and maybe the old shoes will be pressed into service for a while longer. It is this interplay of two psychological forces—intensity of desire and aversion to labor—that is the essence of value, and any attempt to reduce it to a mathematical formula is fatuous; to do so would require an understanding of the inner workings of every individual, under all circumstances, and that calls for omniscience. When a trade is consummated, the psychological forces come to rest, and this objective act is a historical fact that is measurable; that is, the price agreed upon tells us something about what the buyer and seller had been cogitating upon before the trade took place. There is no way of measuring their antecedent emotional experiences. And even then, even after the trade has been consummated, it cannot be said with certainty that it will be repeated. The determination of value in the future is largely guesswork. That is why there are "mark down" sales.

This impossibility of fixing future values is the rock on which "economic planning" founders. Not only is the planner without data on which to base his prognoses, but the plannee himself cannot furnish it. No man can foretell with certainty what he will want at a future time, or how much he will want it, for no man can predict the influences that will determine his decisions. Today he is most anxious to have a hat, but tomorrow he is convinced that headgear causes loss of hair and he decides to go uncovered; or the repair of his roof is a more pressing need than the automobile he had set his heart on; or a lessening of his income compels a reevaluation