Examining the influence of Marx and Sraffa on the theory of money may at first seem paradoxical. In Sraffa's principal work, Production of Commodities by Means of Commodities (1960), the role of money in relation to the 'real' economy of production is nowhere mentioned. He introduces the monetary rate of interest as determining rates of profit without investigating either its origin or the role of money as a price standard. Several of Sraffa's disciples have nonetheless presented analyses of the monetary interest rate, which will be discussed below (in section 2).