Brief description: When aggregate supply falls the supply curve shifts to the left. Here a Keynesian aggregate supply curve is shown.

Detailed description: Keynesians believe that the aggregate supply curve will be the same in the short and long run, and so a decrease in aggregate supply will shift the edge of the curve to the left. This may be caused by a change in productivity, changes in the tax and benefit system or some other factor affecting the amount of output that can be produced in the economy.