Regular readers know that I think the liquidity trap is intriguing and certainly relevant right now, but more of a theoretical curiosity than a hugely important factor. Tyler Cowen makes much the same case in this post, which thinks through the zero lower bound argument by reviewing the importance of substitutability in other markets.
Cowen argues that adjustment can be slow for very close substitutes, but that it will happen - and many other factors are important than just the substitutability of cash and Treasuries for the adjustment process. That's all well and good, but the fact remains that the adjustment process is considerably slower for closer substitutes than it is for substitutes that are much less close. It is precisely the close substitutability of cash and Treasuries that makes all the other issues that Cowen talks about relevant right now, and that is the sense in which the liquidity trap is meaningful. Cowen uses the example of the close substitutability of grapes and pluots to talk about the liquidity trap, and he says that substitutability alone does not explain the adjustment. His appetite, for example, is also a factor. I would only add that we're only even talking about "appetite" as a factor because what is introduced is more food (pluots). If Cowen's house guest had brought, say, a bottle of wine we might think of the wine and the grapes as complements rather than substitutes. "Appetite" in the sense of how much food you feel like eating is no longer a constraint at all, because it might be very nice to have wine and grapes together. The close substitutability of grapes and pluots is disconcerting precisely because it introduces the relevance of other constraints like appetite.
That's largely how I think about the liquidity trap. It makes things problematic that wouldn't be problematic under other circumstances. Other than that, it's hard to stretch this metaphor much farther. Grapes and pluots aren't media of exchange, stores of value, or opportunities for speculation, after all - so I'm not sure how much mileage Cowen thought he was going to get out of this. I suppose it works as an explanation for portfolio adjustment, which is what he claims he's talking about. But since when is the importance of the liquidity trap derived from balancing the composition of your portfolio between cash and bonds? That's not really the major point. The point is the demand for liquidity as well as the impact (or lack of impact) of monetary expansion on the interest rate.
I guess I'd offer one more interpretation to push this metaphor a little further. If you were Cowen's house guest and you knew about his grapes/pluots dilemma, it would probably make more sense for you to bring that bottle of wine that would complement grape consumption, rather than those pluots which would be close substitutes for grapes, right?
What could possible complement liquidity preference right now - what could encourage households and firms to work through their liquidity preference - rather than exascerbate it? Probably some additional aggregate demand, right?
Friday Night Music
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