Sraffa and Keynes on the Concept of Commodity Rates of Interest

This paper considers how Keynes and Sraffa in December 1931 disagreed on the definition of the concept of commodity rate of interest that was to appear in Sraffa's review of Hayek's Prices and Production. An analysis of that disagreement, which emerges from two letters sent by Keynes to Sraffa, also allows us to see that Sraffa's 1932 definition and the definition adopted by Keynes in Chapter 17 of the General Theory are not the same, and to examine the peculiarities of Sraffa's approach and of the definition of commodity rates of interest put forward by Keynes both in his 1931 discussion with Sraffa and in the General Theory.