Similarly, in the realm of monetary policy, the Fed and other central banks certainly don’t slavishly follow prescriptions from any rule. They retain discretion to deviate from such prescriptions when responding to severe shocks, unusually strong headwinds, or significant asymmetric risks.
In the implementation of macroprudential supervision, I believe it will be similarly advantageous to put in place a system of controls in which fixed rules play an important role while a place is preserved for the discretionary judgments of regulators. Fixed rules will  9  See Duffie and others, “Policy Perspectives”, in note 5, for a discussion of these issues.