In June 2015, a committee of Federal Reserve Bank Presidents conducted a “macroprudential tabletop exercise”—a kind of wargame—to determine what tools to use should risks to financial stability arise in an environment when growth and inflation are stable. The conventional wisdom—widely supported in policy pronouncements and in a range of academic studies—is that the appropriate tools are prudential (capital and liquidity requirements, stress tests, margin requirements, supervisory guidance and the like). Yet, in the exercise, the policymakers found these tools more unwieldy and less effective than anticipated. As a result, “monetary policy came more quickly to the fore as a financial stability tool than might have been thought.”

This naturally leads us to ask whether there are circumstances when central bankers should employ monetary policy tools to address financial stability concerns. Making the case for or against use of monetary policy to secure financial stability is usually based on assessing the costs and benefits of a policy that "leans against the wind" (LAW) of financial imbalances...