While writing The General Theory of Employment, Interest, and Money, Keynes had an argument with George Bernard Shaw about Marx. Keynes wrote to Shaw on 1 January 1935:
"...To understand my state of mind, however, you have to know that I believe myself to be writing a book on economic theory, which will largely revolutionise - not, I suppose, at once but in the course of the next ten years - the way the world thinks about economic problems. When my new theory has been duly assimilated and mixed with politics and feelings and passions, I can't predict what the upshot will be in its effects on actions and affairs. But there will be a great change, and, in particular, the Ricardian foundations of Marxism will be knocked away.I don't accept that Marx built on Say's Law, which is what Keynes refuted.
I can't expect you, or anyone else, to believe this at the present stage. But for myself I don't merely hope what I say, - in my own mind I'm quite sure."