"I describe two amplifications mechanisms that operate during liquidity crises and discuss the scope for central bank policies during crises as well as preventive policies in advance of crises. The first mechanism works through asset prices and balance sheets. A negative shock to the balance...

A number of consequences emerge. (i) Fiscal stimulus or \helicopter drops of money" are powerful and, indeed, pull the economy out of the zero lower bound. More generally, the model allows for the joint analysis of optimal monetary and fiscal policy. (ii) The Taylor principle is strongly...