This is Brad DeLong:

An optimizing central bank that cares only about inflation and unemployment because it does not find itself at the zero nominal lower bound and does not fear engaging in nonstandard monetary policy will engage in full fiscal offset: it will take care to make sure that if fiscal policy becomes more stimulative then it will make monetary policy less stimulative by the same amount.

What Brad of course here is expressing is the so-called Sumner Critique – that is the fiscal multiplier will always be zero if the central bank directly or indirectly targets aggregate demand either as a result of an inflation target, an NGDP level target or for that matter a Bernanke-Evans style monetary rule.

Brad has a nice little model to illustrate his point. In some ways Brad’s model is similar to Nick Rowe’s game theoretical discussion of what Brad calls “full fiscal offset” (see my earlier post on the topic here). My simpler IS/LM+ model illustrates the same point (have a look at the model here).

Brad, however, thinks that the fiscal multiplier is positive at the Zero Lower Bound (ZLB):

… this argument breaks down at the zero nominal lower bound. At the zero lower bound the central bank does care only about inflation and unemployment. It cares as well about the magnitude of the non-standard monetary policy measures it must take in order to achieve its net monetary policy impetus value m.

This argument is somewhat harder for me to get. The Zero Lower Bound only exists as a mental construction in the heads of central bankers. Central banks can always ease monetary policy – even if interest rates are close to zero. That is exactly what the Fed and the Bank of Japan are doing at the moment.

Furthermore, it might of course be right that “real world” central banks prefer not to use other instruments rather than interest rates and therefore prefer the government to “push” aggregate demand (hence that is why Brad argues that the “instrument” should enter into the utility function of the central  bank). However, that would still be monetary policy (rather than fiscal policy) as government spending would only impact aggregate demand/NGDP because the central bank chose not to offset the increase in government spending. If the central bank on the other hand used for example a money base rule or McCallum’s MC rule where the policy instrument is a combination of the exchange rate and interest rates then the central bank would not pay any attention to the ZLB.

PS I find it “interesting” to read the comment section on Brad’s blog. It is clear that some of the more ideologically inclined Keynesians have a very hard time accepting the fact that the fiscal multiplier might be zero. (yes, I similarly have a very hard time accepting arguments that it might be positive so I am no saint…)

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This one is pretty funny (HT Daniel Brackins)