‘I have been much pre-occupied with the causation, so to speak, of my progress of mind from the classical position to my present views,—with the order in which the problem developed in my mind. What some people think is an unnecessarily controversial tone is really due to the importance in my own mind of what I used to believe, and of the moments of transition which were for me personally moments of illumination…. You don't mention effective demand or, more precisely, the demand schedule for output as a whole, except in so far as it is implicit in the multiplier. To me the most extraordinary thing, regarded historically, is the complete disappearance of the theory of demand and supply for output as a whole, i.e. the theory of employment, after it had been for a quarter of a century the most discussed thing in economics. One of the most important transitions for me, after my Treatise on Money had been published, was suddenly realising this. It only came after I had enunciated to myself the psychological law that, when income increases, the gap between income and consumption will increase,—a conclusion of vast importance to my own thinking but not apparently, expressed just like that, to anyone else's. Then, appreciably later, came the notion of interest being the measure of liquidity preference, which became quite clear in my mind the moment I thought of it.