This paper shows that it is possible to develop Marx’s categories of new value and surplus value in a consistent model of competitive prices such as Sraffa’s model. In particular, Marx’s theory is interpreted according the "Price of Net Product-Unallocated Purchasing Power Labour Theory of Value" (PNN-UPN LVT) proposed by Duncan Foley and Gerard Duménil. In this framework Marx’s value theory does not lead to inconsistent results. The meaning of this theory, however, cannot rely only on considerations about the formal characteristics of the model. From the one hand, some aspects of this meaning can ensue, from a comparison with the theory of "the monetary circuit", because of the role that the PNN-UPN LTV attributes to money and to ‘the monetary expression of the labor time’ and of the role played by monetary wages in the "circuit". From the other hand, it is important a comparison with the path Sraffa followed in developing his model of prices. In particular it is relevant Sraffa’s choice of the units of measure of labor and prices in consequence of the ‘transformation’ of the wage rate from a determined basket of commodity to a share of the net product. It is possible to suggest a line of research aiming at integrating Sraffa’s model of prices and the theory of the monetary circuit via Marx, or the interpretation of Marx’s theory put forward by Duncan Foley and Gerard Duménil.
Keywords: Marxian economics; Theory of value and surplus value; Value of money; Monetary circuit.
Jel Code: B51; E11