This comment is jointly authored by Stephen G. Cecchetti and Sir Paul M.W. Tucker.

Central banks have been reinvented over the past decade, first in response to the financial crisis, and then as a consequence of Covid-19. While trying to maintain monetary stability and promote economic recovery, their balance sheets have ballooned. In 2007, the central banks in the United States, euro area, United Kingdom, and Japan had total assets from 6% to 20% of nominal GDP. By the end of 2020, the Fed’s balance sheet was 34% of GDP, the ECB’s 59%, the Bank of England’s 40%, and the Bank of Japan’s 127%.

Before it is possible to consider how well this worked, it is necessary to be clear about what policymakers’ various operations were trying to achieve. Headline declarations of aiming at “price stability” or “financial stability” are unsatisfactory as they jump to end goals without attending to the motivations for specific operations and facilities. The case of the Fed is illustrative. Among other things, they bought U.S. Treasury bonds, offered to purchase commercial paper, corporate and municipal bonds, and set up facilities to lend directly to real-economy businesses as well as to securities dealers. These cannot be assessed solely on whether, alone or together, each materially improved the outlook for economic activity and inflation.

Without a sense of the intended purpose of each central bank action, it is difficult for political overseers or interested members of the public to hold central banks accountable. Precisely because central banks are independent (rightly in our view), that accountability takes the form of public scrutiny and debate. But we argue that it is also hard for central bankers themselves to do their jobs unless they distinguish carefully—in internal deliberations, and external communication—the rationale for different interventions….