<P> The production of commodities creates, and is the one and universal cause that creates a market for the commodities produced . </P> <P> Keynes does not cite a specific source for the phrase, and, as it does not appear to be found in the pre-Keynesian literature, some consider its ultimate origin a "mystery". The phrase "supply creates its own demand" appears earlier, in quotes, in a 1934 letter of Keynes, and has been suggested that the phrase was an oral tradition at Cambridge, in the circle of Joan Robinson, and that it may have derived from the following 1844 formulation by John Stuart Mill: </P> <P> Nothing is more true than that it is produce which constitutes the market for produce, and that every increase of production, if distributed without miscalculation among all kinds of produce in the proportion which private interest would dictate, creates, or rather constitutes, its own demand . </P>

Who said supply creates it's own demand