Say's law, or the law of market, is an economi c pri nci pl e of cl assi cal economics named after the French busi nessman and e conomi st Jean-Baptiste Say (1767-1832), who stated that 'supply creates its own demand'. 'Suppl y creates i ts own demand' is the formulation of Say's law by John Maynard Keynes. The rejection of this doctrine is a central component of The General Theory of Employment, Interest and Money (1936) and a central tenet of Keynesian economics