The Collaboration between J. M. Keynes and R. F. Kahn from the Treatise to the General Theory

There is no greater satisfaction than in the exchanging of ideas between minds which have truly met, leading to further discoveries and a shift of view in response to difficulties and objections.

—John Maynard Keynes

Of all the economists in John Maynard Keynes's circle, Richard Kahn was perhaps closer to him than any other when he was working on the General Theory. However, the precise contribution he made to the development of the ideas that were to become the General Theory is still much debated.

On the one hand we have Donald Moggridge (1994, 109; 1992, 532 n), who argues that in subsequent reconstructions Kahn credited himself and the “Circus” with a decisive role in the evolution of Keynes's theory, although the writings offer no evidence or documentation to support the claim. On the other hand we have Joseph Schumpeter (1954, 1172), who saw the collaboration with Kahn as something very close to “co-authorship,” while Roy Harrod (1951, 451) described Kahn as Keynes's “main pillar support” in the work on the book.

Most interpretations have tended to place considerable stress on the difficulty of assessing the exact nature of the collaboration between Keynes and Kahn. “Kahn's role has provoked intermittent speculation,” writes Peter Clarke (1988, 249). Robert Skidelsky (1992, 449) observes that “the nature of Kahn's contribution to Keynes's thinking is much disputed.” And Don Patinkin (1993, 652 n. 5) refers to “the perennial question of Richard Kahn's role in the writing of the General Theory.”

In this essay I take a new look at the question in light of the correspondence between Keynes and Kahn, with the aim expressed in the title of this article: to read the transition from the Treatise to the General Theory as a history of collaboration.¹

Keynes's “Favourite Pupil”

Kahn met Keynes as a student at King's College for weekly supervision in the year when—having achieved somewhat modest results in the natural science tripos—he still had a further year's scholarship available and set about studying for the economics tripos, which he passed with brilliant results in June 1928.

As we know, Keynes was struck by the student's flair from the very outset. Keynes wrote in the margin of a paper by Kahn of 4 November 1927 that “I think you have a real aptitude for Economics” (RFK XI/3).² A few months later, on 27 April 1928, his comment on another essay ran: “Very good—almost a perfect answer” (RFK XI/3). Two days later he wrote to his wife, Lydia, “Yesterday my favourite pupil Kahn wrote me one of the best answers I ever had from a pupil—he must get a first class” (JMK PP/45/190:4).³

In fact, the correspondence as we have it now begins with the letter Keynes sent Kahn on the publication of the tripos results: “My dear Kahn, very warm congratulations that all was, after all, well in the exams—though, as you know, I expected it” (15-6-1928; RFK 13/57:1).

The thesis Kahn wrote between October 1928 and December 1929 to obtain a fellowship at King's was again the happy outcome of initial failure—this time to gain access to the Midland Bank's monetary statistics. According to Kahn (1989, x), Keynes “at that time was still a staunch believer in the Quantity Theory of Money as an expression of causation” and thought that the data could offer good material for his pupil's dissertation. Since the data could not be used, Kahn's account continues, “Keynes then left me to choose my own subject. Under the influence of Marshall's Principles, I chose the Economics of the Short Period. In making my choice I was encouraged by Shove...