<P> Say's law, or the law of markets, in classical economics, states that aggregate production necessarily creates an equal quantity of aggregate demand . The French economist Jean - Baptiste Say (1767--1832) introduced the idea in 1803, in his principal work, A Treatise on Political Economy (Traité d'économie politique): </P> <P> A product is no sooner created, than it, from that instant, affords a market for other products to the full extent of its own value . </P>

​say's law is a doctrine which states