<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> 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>
​ say 's law is a doctrine which states
​ say 's law is a doctrine which states
aggregate production necessarily creates an equal quantity of aggregate demand
aggregate production necessarily creates an equal quantity of aggregate demand