Supply and demand track each other

Say’s Law versus Keynesian Economics

Say’s Law, as explicated by the great liberal political economist Jean-Baptiste Say (1767-1832), is the principle that supply constitutes demand, with the corollary that aggregate supply always equals aggregate demand. There’s no more important principle in political economy to get perfectly right – and assiduously avoid getting wrong – than Say’s Law.

They are never equal, but at any given moment the adjustment to supply or demand should make them more equal than last time.  There is always a market uncertainty.

The use of central bank money implies a wedge fee in the cost of making supply tend toward demand. If the central bank operates like a monopsony, then that wedge fee further separates supply and demand.