Keynes began working on the Treatise during the summer of 1924 at Tilton. Dennis Robertson was there for a visit during the early stages.

For the period 1924–5, we know no more about the development of Keynes's ideas than from the material presented in Volume XIII (pp. 15–43) until he began his long series of letters to Lydia. Written almost daily whenever they were apart, these run from October 1925 until his illness in 1937. They form the basis of the statements in this section. In the first, dated 18 October, he mentioned receiving the final version of Robertson's Banking Policy and the Price Level. The next day, he said that it would probably be another fortnight before he got back to his book, but there was no mention of his doing anything beyond ‘some philosophical passages about love of Money’ (6 November) until the end of the next month.

From a letter to LYDIA KEYNES, 27 November 1925

This morning I had nothing to do!–so I took out the basket where my book lives and admired its table of contents. Then I read the first chapter. This needed a reference to my manuscript on ancient currencies. But when that was taken out, I was a lost man and spent the rest of the morning trying to remember my theories about Greek and Babylonian affairs. I feel drawn to waste a little more time over these things.