WITH THE STUDY OF problems of capitalization, credit, and discount, the peaceful parade of equationally determinate barter economy' comes to an abrupt halt. The systems of equations expressing the conditions of equilibrium theory differ in number from the unknowns to be determined. Equational determinacy is established only by the introduction of money into the system. This conclusion is, I believe, novel in general-equilibrium theory. It is an obvious confirmation to an essentially monetary theory of interest-as distinguished from a real capital theory admitting of short-run monetary dislocations. In its support, demonstration of the following subordinate propositions will be attempted: In a static, but not stationary,2 barter economy it is necessary, first, to posit a plurality of interest rates in order to secure the equality of demand and supply of loans for each of the various goods and services lent in natura.3 It is necessary, second, to provide for yet another plurality of discount rates, to take account of the loan aspect of payments for services made at times other than those at which their final products are sold. It is necessary, third, to establish various fixed relationships, which I call capitalization rates, between the prices of services and the prices of the goods which are their sources, so that individuals may be able to choose rationally between the purchase (sale) of the goods and the purchase (sale) of the services. Under barter, there are no clear interrelationships between these various rates. The lack of interrelationships renders indeterminate each of the three