Via Scott Sumner I found another of Nick Rowe’s remarkably thoughtful and thought-provoking posts about the foundations of monetary theory. The object – at least as I read him – of Nick’s post is to explain how and why money can (or must) be neutral. And Nick performs this little (or maybe not so little) feat by juxtaposing two giants in the history of monetary theory, David Hume from the eighteenth century and Don Patinkin from the twentieth. Both, it seems, were convinced of the theoretical, indeed logical, necessity of monetary neutrality, but both felt constrained by observational experience to acknowledge that money has real effects, which is just another of saying that money is not (or at least not always) neutral.
I am not going to discuss Nick’s post in detail. Instead, I want to question what I take to be an underlying premise of his post, that there is a theoretical presumption that money is neutral, at least in the long run. In questioning the neutrality of money, I do not mean that one cannot easily write down a model in which it is possible to derive the conclusion that a change in the quantity of money changes the equilibrium in that model by changing all money prices proportionately, leaving all relative prices and all real quantities of goods produced and consumed unchanged. What I assert is that the real world conditions under which this result would obtain do not exist, with the possible exception of a currency reform in which a new currency unit is introduced to replace the old unit at a defined rate between the new and old units. In such a case, but only in such a case, it is likely that the results of the change would be confined to money prices, with no effect on real quantities. (It is because of this trivial exception that I inserted asterisks after “always” and “everywhere” in the title of this post.)
Let me give a few, certainly not all, of the reasons why money is never neutral. First, most agree as David Hume explained over 250 years ago that changes in the quantity of money do have short-term real effects. The neutrality of money is thus usually presented as a proposition valid only in the long-run. But there is clearly no compelling reason to think that it is valid in the long run either, because, as Keynes recognized, the long run is a succession of short runs. But each short-run involves a variety of irreversible investments and irrevocable commitments, so that any deviation from the long-run equilibrium path one might have embarked on at time 0 will render it practically impossible to ever revert back to the long-run path from which one started. If money has real short-term effects, in an economy characterized by path dependence, money must have long-term effects. Real irreversible investments are just one example of such path dependencies. There are also path dependencies associated with investments in human capital or employment decisions. Indeed, path dependencies are inherent in any economy in which trading is allowed at disequilibrium prices, which is to say every economy that exists or ever existed.
If workers’ chances of being employed depend on their previous employment history, short-term increases in employment necessarily have long-term effects on the future employability of workers. Chronic high employment now degrades the quality of the labor force in the future. If arguments that potential GDP has fallen since 2008 have any validity, a powerful reason why potential GDP has fallen is surely the increase in chronic unemployment since 2008.
Another way to make this point is that the proposition of long-run neutrality presupposes that there is one and only one equilibrium time path for the economy. The economy is in equilibrium if and only if it is on that unique time path. Under long-run neutrality, you can deviate from that equilibrium time path for a while, but sooner or later you must get back on it. When you’re back on it, monetary neutrality has been restored. But if there is no single equilibrium time path, there is no presumption of neutrality in the short run or the long run.
Let me also mention another reason besides time dependence and irreversibility why it is a mistake to conceive of an economy as having a unique equilibrium time path. As I have observed in previous posts on this blog, every economic equilibrium is dependent on the expectations held by the agents. A change in expectations changes the equilibrium. Or, as I have expressed it previously, expectations are fundamental. If a change in monetary policy induces, or is associated with, a change in expectations, the economic equilibrium changes. So money can’t be neutral. Ever.
PS Let me just mention that I have drawn in this post on an unpublished paper by Richard Lipsey “The Neutrality of Money,” which he was kind enough to share with me. Lipsey particularly emphasized path dependence as a reason why money, as he put, “is an artifact of economic models,” not a universally correct prediction about the world. Lipsey developed the idea of path dependence more fully in another much longer paper co-athored with Kenneth Carlaw that he shared with me, “Does History Matter? Empirical Analysis of Evolutionary versus New Classical Views of the Economy” forthcoming in the Journal of Evolutionary Economics. Perhaps in a future post, I will discuss the Carlaw Lipsey paper at greater length.