Say's law
Keynesian economists, such as Paul Krugman, stress the role of money in negating Say's law: Money that is hoarded (held as cash or analogous financial instruments) is not spent on products. To increase monetary holdings, someone may sell products or labor without immediately spending the proceeds. This can be a general phenomenon: from time to time, in response to changing economic circumstances, households and businesses in aggregate seek to increase net savings and thus decrease net debt. To increase net savings requires earning more than is spent—contrary to Say's law, which postulates that supply (sales, earning income) equals demand (purchases, requiring spending). Keynesian economists argue that the failure of Say's law, through an increased demand for monetary holdings, can result in a general glut due to falling demand for goods and services.