A letter from Friedrich Hayek to Joan Robinson, dated March 10, 1941, quoted in Konstantinos Repapis’s paper “Hayek’s business cycle theory during the 1930’s: A critical account of its development:
“My present pre-occupation with what may seem altogether different problems [than technical issues of the business cycle] may suggest to you that I am running away from the difficulties which my position creates. The fact is that I have increasingly come to the conclusion that all our differences — or I should probably say my differences with almost all “modern” economists not only in the specific field of monetary theory but quite generally, including in particular the approach to the theory of competition, the use of concepts representing averages or aggregates, and the whole problem of socialism, all trace back to a more fundamental difference which I am gradually trying to clear up. The only published results of these efforts gradually to work out a consistent system of “subjectivism” is the article on “Economics and Knowledge” in Economica 1937 which you may have seen. But I feel that to elaborate these fundamental problems is more important than to go on with the work on particular problems where one comes up all the time against the same difficulties…” (Hayek’s letter, 10 March 1941)
What Hayek was then working on was his “Scientism and the Study of Society” papers. I have long argued that these papers were as much targeted at Keynes and Keynesian/ Cambridge economics as they were at anything else.
The correspondence between Friedrich Hayek and Joan Robinson is archived at Kings College, Cambridge, and has yet to be published.