The Genesis of the Only Diagram in the General Theory

It is well known that the General Theory contains only one diagram, this occurring in chapter 14 criticising the orthodox theory of the rate of interest. Attached to the diagram is a footnote containing an acknowledgement: “This diagram was suggested to me by Mr. R.F. Harrod†(CW VII, p. 180). The impression conveyed by this remark is that Harrod drew the diagram and offered it to Keynes, who then accepted and used it. Further enquiry into the diagram's origins reveals the existence of an initial version which grew out of correspondence between Keynes and Harrod in August-September 1935 (CW XIII, pp. 526-63). Two of Harrod's writings–his (1951) Keynes biography and a letter to Hawtrey in 1951–imply that he was the author of the initial version, and that this was essentially the same as the published version. And, in seeming corroboration of Harrod's comments, there is the virtual equivalence of the initial version given in The Collected Writings of John Maynard Keynes (CW XIII, p. 557) and the final version printed in the General Theory (CW VII, p. 180J. Taken individually and collectively, these items of evidence all point in the same direction. They support the reasonable inference that, apart from trivial changes in lettering, Harrod was the sole author and creator of the initial and final versions of the diagram, and that Keynes was merely the recipient.