Capital as a Single Magnitude and the Orthodox Theory of Distribution in Some Writings of the Early 1930s

Some writings of the early 1930s by Dennis Robertson and John Hicks present, with a clarity not easily found elsewhere, the reasons why marginalist economists, who until recent decades normally treated capital as a single magnitude, were in fact compelled to do so. This paper focuses on a first reason that emerges from these writings: namely the fact that only this treatment of capital can lend plausibility to the notion of substitutability between factors of production on which the orthodox theory of distribution is built.