Mainly for macroeconomists
There are a significant group of people who think that monetary policy must be the right answer even in a liquidity trap because of the centrality of money in macroeconomics, and because of ‘basic’ ideas like money neutrality. Call them market monetarists if you like. They dislike fiscal stimulus because - in their view - it just has to be second best, or a fudge, compared to monetary policy. Their view is not ideological, but essentially based on macro theory. Now it may not be very relevant to the real world, but for many holding the theoretical high ground is important, because it colours their view of the real world.
That is the group that Paul Krugman has been arguing with recently, and why the point he made in his post yesterday is so critical. It is set in an idealised two period world where Ricardian Equivalence holds, but that is entirely appropriate for the task in hand. If people believe something because of (in their view) basic theory, and you think they are wrong in terms of basic theory, then that is the level on which to argue.
The argument is that in a liquidity trap, when prices are sticky, temporarily expanding the money supply - even if it involves helicopter money (i.e. money financed tax cuts) - will not do anything to get you out of the trap. Another, and more modern, way of saying the money supply increase is temporary is saying that the inflation target is unchanged, so the long run price level is unchanged. (Long run money neutrality does hold in this world.) I will not go through Paul’s argument in detail - I have gone through the same logic before. The basic point is that the temporary increase in money is saved, not spent, because agents know it is temporary. Short run money neutrality does not hold, and not because prices are sticky, but because of Ricardian Equivalence.
It is exactly the same reason why the Pigou effect is no longer discussed. Ricardian Equivalence killed the Pigou effect as a fundamental theoretical idea. If the inflation target is unchanged, when prices fall today the future price level must fall pari passu, reducing the future nominal stock of money. There is no wealth effect. As I noted here, even allowing money to be special in not being redeemable does not get the Pigou effect back, because with irredeemable money any wealth effect comes from the long run stock of money.
Money is not a hot potato in this world. The potato has gone cold because of the liquidity trap, and the money is happily saved to pay the future tax increases that will be required to keep the long run money stock (and price level) constant.
While in this largely frictionless world money is impotent, additional government spending is a foolproof way of expanding demand. So is raising the long run price level, which means at some point raising the inflation target.
All I really wanted to do in this post was make an observation. The theoretical point that Paul makes depends crucially on thinking in an intertemporal manner, which gives you Ricardian Equivalence. Just as price rigidity kills short run monetary neutrality, so does Ricardian Equivalence in an inflation targeting liquidity trap world. So here is modern microfounded macroeconomic theory providing support to increasing government spending rather than monetary policy in a liquidity trap. Modern theory is not inherently anti-Keynesian. .