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):
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.
and
As each of us can only purchase the productions of others with his own productions – as the value we can buy is equal to the value we can produce, the more men can produce, the more they will purchase.