Sraffa’s Correspondence

In February 1968, Sraffa received a letter from a German student, Rudiger Soltwedel, asking him about the meaning and purpose of his equations, which were a riddle to him, having been educated in the marginalist mode of thinking.

As regards your own interpretation, I must say frankly that you have gone astray the moment you speak of “equilibrium” or of “elasticity of factor supply”: all the quantities considered are what can be observed by taking a photograph. There are no rates of change, etc. This point of view was that of the classical economists (e.g. Ricardo), whereas supply & demand curves were introduced in the middle of the 19th century. Economists are now obsessed with them and cannot think without them. My chapter V which gives you such a headache, could be understood as an attempt to solve a problem set by Ricardo, and which I described in my Introduction (sections IV & V) of Vol. I of the Works of Ricardo, 1951. (Sraffa Papers, C 294, 2)

In this letter the metaphor of the photograph is used precisely in the sense expounded in the preface of Sraffa’s 1960 book when specifying the difference between the classical and the marginalist approach to the theory of value and distribution. The classical economists from Adam Smith to Ricardo explained the rate of profits (the real wage rate) and relative prices in terms of a given system of production in use and a given real wage rate (a given rate of profits). The sense also conforms to the one given by Roncaglia: we do have on the one hand a set of given facts (explananS) and on the other a set of magnitudes (wage rate, rate of profits, relative prices) whose relationships are to be determined (explanandum). These relationships define the “mathematical properties” (Sraffa, 1960, 23) of the system of production under consideration and thus how a change in one variable (e.g., the wage rate) implies corresponding changes in the other variables (the rate of profits, prices).¹⁷

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