But psychic quantities can only be felt. They are entirely personal, and there is no semantic means to express their intensity and to convey information about them to other people. There is no method available to construct a unit of value. Let us remember that two units of a homogeneous supply are necessarily valued differently. In the market society there are money prices.
Economic calculation is calculation in terms of money prices.
The various quantities of goods and services enter into this calculation with the amount of money for which they are bought and sold on the market or for which they could prospectively be bought and sold. It is a fictitious assumption that an isolated self-sufficient individual or the general manager of a socialist system, i.e., a system in which there is no market for means of production, could calculate. There is no way which could lead one from the money computation of a market economy to any kind of computation in a nonmarket system. The Theory of Value and Socialism Socialists, Institutionalists and the Historical School have blamed economists for having employed the imaginary construction of an isolated individual's thinking and acting. This Robinson Crusoe pattern, it is asserted, is of no use for the study of the conditions of a market economy.