The Foundations of a Mathematical Theory of Exchange

ECONOMICS is, at the moment, the only member of the group of social sciences which has definitely passed from the qualitative to the quantitative phase. In the words of Professor Hogben,2 political economy . . . is adopting quantitative methods and assuming the ethical neutrality of an exact science." In common with all exact sciences, the science of economics has two branches: (a) the empirical branch (descriptive economics), and (b) the rational branch (pure economic theory). The empirical branch arises first and, by experiment or by observation of actual phenomena, empirical facts are collected and arranged. After a time it becomes necessary to construct the rational branch in order to co-ordinate and interpret the empirical facts already obtained. The rational branch starts from a set of initial propositions which are laid down in advance and to which are applied the processes of deductive reasoning, i.e. formal logic and its specialised extension, mathematical analysis. Some sections of pure economic theory, e.g. the general considerations of exchange and production, are concerned with complex operations involving magnitudes and with a large number of mutually dependent variables. In these sections formal logic is almost powerless, and it is necessary to employ the highly developed extension of logic known as mathematical analysis.3 Now mathematical theories cannot be