Friedman provided a theory for NGDP targeting
A distinct feature of Market Monetarist thinking is that our starting point for monetary analysis is nominal income and that monetary policy determines nominal income or nominal GDP (NGDP). This is contrary to New Keynesian analysis where monetary policy determines real GDP, which in turn determines inflation via a Phillips curve. Hence, to Market Monetarists the split between prices and quantities is not a monetary matter. Monetary policy determines NGDP and that is all that monetary policy can do. While we acknowledge that there is a high correlation between real GDP and NGDP in the short-run the causality runs from NGDP to RGDP and not the other way. In the long run inflation is determined as a residual between NGDP, which is a monetary phenomenon, and RGDP, which is determined by supply side factors. Milton Friedman came to the same conclusion 40 years ago. In a much overlooked (or should I say a forgotten) article from 1971 “A Monetary Theory of Nominal Income” he discusses this topic. The paper is a follow up on “Milton Friedman’s Monetary Framework” in which Friedman discusses his monetary framework with his critics. I have always felt that he failed to explain what he really meant in his “Monetary Framework”. Friedman seems to have realised that himself and his 1971 try to make up this failure. Here is Friedman: “In … "A Theoretical Framework for Monetary Analysis," I outlined a simple model of six equations in seven variables that was consistent with both the quantity theory of money and the Keynesian income-expenditure theory…The difference between the two theories is in the missing equation the quantity theory adds an equation stating that real income is determined outside the system (the assumption of "full employment"); the income-expenditure theory adds an equation stating that the price level is determined outside the system (the assumption of price or wage rigidity)…The present addendum to my earlier paper suggests a third way to supply the missing equation. This third way involves bypassing the breakdown of nominal income between real income and prices and using the quantity theory to derive a theory of nominal income rather than a theory of either prices or real income. While I believe that this third way is implicit in that part of my theoretical and empirical work on money that has been concerned with short-period fluctuations, I have not heretofore stated it explicitly. This third way seems to me superior to the other two ways as a method of closing the theoretical system for the purpose of analyzing short-period changes. At the same time, it shares some of the defects common to the other two ways that I listed in the earlier paper.” Hence, Friedman here acknowledges that the problem in the “Framework” papers was that he tried to come up with a monetary theory that followed a Keynesian route from RGDP to prices rather than “bypassing the breakdown of nominal income between real income and prices and using the quantity theory to derive a theory of nominal income”. This is something completely lost in modern macroeconomic thinking, which see monetary policy working through a Phillips curve. This is somewhat odd given the weak empirical foundation for the existence of a Phillips curve. I will not get into the details of Friedman’s model, but I would note that it could be interesting to see how it would look in a rational expectations version. Back to Friedman: “I have not, before this, written down explicitly the particular simplification I have labeled the monetary theory of nominal income-although Meltzer has referred to the theory underlying Anna Schwartz's and my Monetary History as a "theory of nominal income" (Meltzer 1965, p. 414). But once written down, it rings the bell, and seems to me to correspond to the broadest framework implicit in much of the work that I and others have done in analyzing monetary experience. It seems to me also to be consistent with many of our findings. I do not propose here to attempt a full catalog of the findings, but I should like to suggest a number and, more important, to indicate the chief defect that I find with the framework.” Here Friedman acknowledges that his empirical work for example on the Great Depression is based on a monetary theory of nominal income rather than on a quasi-Keynesian model (like the one he presents in his "Framework"). Any Market Monetarist would of course agree that a monetary theory of nominal income is needed to explain the Great Depression and the Great Recession for that matter. Friedman continues: “One finding that we have observed is that the relation between changes in the nominal quantity of money and changes in nominal income is almost always closer and more dependable than the relation between changes in real income and the real quantity of money or between changes in the quantity of money per unit of output and changes in prices. This result has always seemed to me puzzling, since a stable demand function for money with an income elasticity different from unity led me to expect the opposite. Yet the actual finding would be generated by the approach of this paper, with the division between prices and quantities determined by variables not explicitly contained in it.” This empirical result is highly interesting – the correlation between money and NGDP is stronger than between money and prices and income. In that regard it seems odd that Friedman never endorsed NGDP targeting – after all it would be natural to endorse a monetary policy rule that actually is directed towards something monetary policy can determine. However, there is no doubt that Friedman’s 1971 paper clearly provides the theoretical foundation for NGDP targeting. It is only too bad Friedman never came to that conclusion. Finally I should say that Market Monetarists like David Beckworth and Josh Hendrickson are working on developing a modern monetary theory of nominal income determination. PS Scott Sumner in a recent comment also discuss the relationship between NGDP, prices and quantities in Keynesian and (Market) Monetarist models. PPS It should be noted that Bennett McCallum in a number of papers refers to Friedman's 1971 paper when he argues in favour of nominal income targeting. See for example "Nominal Income Targeting in an Open-Economy Optimizing Model"