Finding out the prices of a large range of commodities is itself a costly enterprise, and knowledge of this fact by price setters is itself enough to… - Kenneth Arrow

Property systems are in general not completely self-enforcing. They depend for their definition upon a constellation of legal procedures, both civil and criminal. The course of the law itself cannot be regarded as subject to the price system. The judges and the police may indeed be paid, but the system itself would disappear if on each occasion they were to sell their services and decisions. Thus the definition of property rights based on the price system depends precisely on the lack of universality of private property and of the price system. This ties in with the third hypothesis put forward in section I. The price system is not, and perhaps in some basic sense cannot be, universal. To the extent that it is incomplete, it must be supplemented by an implicit or explicit social contract. Thus one might loosely say that the categorical imperative and the price system are essential complements.

If the state of information (the set of signals received) is given and constant, then optimal choice is a problem of decision making under a given uncertainty, a situation that has been the subject of considerable analysis in the last thirty years. The problems of the economics of information proper arise when the probability distribution of states of the world is a variable. In the language adopted here, the signals received can vary. The existence of signals creates two important possibilities for the improvement of decision making. The first is taking advantage of the existence of signals. If the individual knows that a signal will be received before the decision has to be made, his optimal choice should be a function of the signal. We can think, alternatively but equivalently, of making the decision after the receipt of the signal and basing it on the probability distributions of consequences conditional on the signal, or of making the decision in advance for all possible values of the signal.

Speaking very broadly, almost any human action involves choice; the external environment delimits a range of possible actions at any given moment but does not usually reduce that range to a single alternative. The formulation of a theory of human action in some sphere as a theory of choice means its presentation as a functional relation associating with each possible range of alternatives a chosen one among them.