Ludwig von Mises
On the Development of the Subjective Theory of Value
2. Preferring as the Basic Element in Human Conduct
All conscious conduct on the part of men involves preferring an A to a B. It is an act of choice between two alternative possibilities that offer themselves. Only these acts of choice, these inner decisions that operate upon the external world, are our data. We comprehend their meaning by constructing the concept of importance. If an individual prefers A to B, we say that, at the moment of the act of choice, A appeared more important to him (more valuable, more desirable) than B.
We are also wont to say that the need for A was more urgent than the need for B, This is a mode of expression that, under certain circumstances, may be quite expedient. But as an hypostatization of what was to be explained, it became a source of serious misunderstandings. It was forgotten that we are able to infer the need only from the action. Hence, the idea of an action not in conformity with needs is absurd. As soon as one attempts to distinguish between the need and the action and makes the need the criterion for judging the action, one leaves the domain of theoretical science, with its neutrality in regard to value judgments. It is necessary to recall here that we are dealing with the theory of action, not with psychology, and certainly not with a system of norms, which has the task of differentiating between good and evil or between value and worthlessness. Our data are actions and conduct. It may be left undecided how far and in what way our science needs to concern itself with what lies behind them, that is, with actual valuations and volitions. For there can be no doubt that its subject matter is given action and only given action. Action that ought to be, but is not, does not come within its purview.
This best becomes clear to us if we consider the task of catallactics. Catallactics has to explain how market prices arise from the action of parties to the exchange of goods. It has to explain market prices as they are, not as they should be. If one wishes to do justice to this task, then in no way may one distinguish between "economic" and "noneconomic" grounds of price determination or limit oneself to constructing a theory that would apply only to a world that does not exist. in Böhm-Bawerk's famous example of the planter's five sacks of grain, there is no question of a rank order of objective correctness, but of a rank order of subjective desires.
The boundary that separates the economic from the noneconomic is not to be sought within the compass of rational action. It coincides with the line that separates action from nonaction. Action takes place only where decisions are to be made, where the necessity exists of choosing between possible goals, because all goals either cannot be achieved at all or not at the same time. Men act because they are affected by the flux of time. They are therefore not indifferent to the passage of time. They act because they are not fully satisfied and satiated and because by acting they are able to enhance the degree of their satisfaction. Where these conditions are not present?as in the case of "free" goods, for example?action does not take place.