The history of economics society is holding its annual meeting in Chicago from Friday June 15 to Sunday June 17. Bringing together material from a number of posts over the past five years or so about Keynes and the Fisher equation and Fisher effect, I will be presenting a new paper called “Keynes and the Fisher Equation.” Here is the abstract of my paper.

One of the most puzzling passages in the

General Theoryis the attack (GT p. 142) on Fisher’s distinction between the money rate of interest and the real rate of interest “where the latter is equal to the former after correction for changes in the value of money.” Keynes’s attack on the real/nominal distinction is puzzling on its own terms, inasmuch as the distinction is a straightforward and widely accepted distinction that was hardly unique to Fisher, and was advanced as a fairly obvious proposition by many earlier economists including Marshall. What makes Keynes’s criticism even more problematic is that Keynes’s own celebrated theorem in theTract on Monetary Reformabout covered interest arbitrage is merely an application of Fisher’s reasoning inAppreciation and Interest. Moreover, Keynes endorsed Fisher’s distinction in theTreatise on Money. But even more puzzling is that Keynes’s analysis in Chapter 17 demonstrates that in equilibrium the return on alternative assets must reflect their differences in their expected rates of appreciation. Thus Keynes, himself, in theGeneral Theoryendorsed the essential reasoning underlying the distinction between real and the money rates of interest. The solution to the puzzle lies in understanding the distinction between the relationships between the real and nominal rates of interest at a moment in time and the effects of a change in expected rates of appreciation that displaces an existing equilibrium and leads to a new equilibrium. Keynes’s criticism of the Fisher effect must be understood in the context of his criticism of the idea of a unique natural rate of interest implicitly identifying the Fisherian real rate with a unique natural rate.

And here is the concluding section of my paper.

Keynes’s criticisms of the Fisher effect, especially the facile assumption that changes in inflation expectations are reflected mostly, if not entirely, in nominal interest rates – an assumption for which neither Fisher himself nor subsequent researchers have found much empirical support – were grounded in well-founded skepticism that changes in expected inflation do not affect the real interest rate. A Fisherian analysis of an increase in expected deflation at the zero lower bound shows that the burden of the adjustment must be borne by an increase in the real interest rate. Of course, such a scenario might be dismissed as a special case, which it certainly is, but I very much doubt that it is the only assumptions leading to the conclusion that a change in expected inflation or deflation affects the real as well as the nominal interest rate.

Although Keynes’s criticism of the Fisher equation (or more precisely against the conventional simplistic interpretation) was not well argued, his intuition was sound. And in his contribution to the Fisher festschrift, Keynes (1937b) correctly identified the two key assumptions leading to the conclusion that changes in inflation expectations are reflected entirely in nominal interest rates: (1) a unique real equilibrium and (2) the neutrality (actually superneutrality) of money. Keynes’s intuition was confirmed by Hirshleifer (1970, 135-38) who derived the Fisher equation as a theorem by performing a comparative-statics exercise in a two-period general-equilibrium model with money balances, when the money stock in the second period was increased by an exogenous shift factor* k*. The price level in the second period increases by a factor of *k* and the nominal interest rate increases as well by a factor of *k*, with no change in the real interest rate.

But typical Keynesian and New Keynesian macromodels based on the assumption of no capital or a single capital good drastically oversimplify the analysis, because those highly aggregated models assume that the determination of the real interest rate takes place in a single market. The market-clearing assumption invites the conclusion that the rate of interest, like any other price, is determined by the equality of supply and demand – both of which are functions of that price — in that market.

The equilibrium rate of interest, as C. J. Bliss (1975) explains in the context of an intertemporal general-equilibrium analysis, is not a price; it is an intertemporal rate of exchange characterizing the relationships between all equilibrium prices and expected equilibrium prices in the current and future time periods. To say that the interest rate is determined in any single market, e.g., a market for loanable funds or a market for cash balances, is, at best, a gross oversimplification, verging on fallaciousness. The interest rate or term structure of interest rates is a reflection of the entire intertemporal structure of prices, so a market for something like loanable funds cannot *set* the rate of interest at a level inconsistent with that intertemporal structure of prices without disrupting and misaligning that structure of intertemporal price relationships. The interest rates quoted in the market for loanable funds are determined and constrained by those intertemporal price relationships, not the other way around.

In the real world, in which current prices, future prices and expected future prices are not and almost certainly never are in an equilibrium relationship with each other, there is always some scope for second-order variations in the interest rates transacted in markets for loanable funds, but those variations are still tightly constrained by the existing intertemporal relationships between current, future and expected future prices. Because the conditions under which Hirshleifer derived his theorem demonstrating that changes in expected inflation are fully reflected in nominal interest rates are not satisfied, there is no basis for assuming that a change in expected inflation affect only nominal interest rates with no effect on real rates.

There are probably a huge range of possible scenarios of how changes in expected inflation could affect nominal and real interest rates. One should not disregard the Fisher equation as one possibility, it seems completely unwarranted to assume that it is the most plausible scenario in any actual situation. If we read Keynes at the end of his marvelous Chapter 17 in the *General Theory* in which he remarks that he has abandoned the belief he had once held in the existence of a unique natural rate of interest, and has come to believe that there are really different natural rates corresponding to different levels of unemployment, we see that he was indeed, notwithstanding his detour toward a pure liquidity preference theory of interest, groping his way toward a proper understanding of the Fisher equation.

In my

Treatise on MoneyI defined what purported to be a unique rate of interest, which I called thenatural rateof interest – namely, the rate of interest which, in the terminology of myTreatise, preserved equality between the rate of saving (as there defined) and the rate of investment. I believed this to be a development and clarification of of Wicksell’s “natural rate of interest,” which was, according to him, the rate which would preserve the stability of some, not quite clearly specified, price-level.I had, however, overlooked the fact that in any given society there is, on this definition, a

differentnatural rate for each hypothetical level of employment. And, similarly, for every rate of interest there is a level of employment for which that rate is the “natural” rate, in the sense that the system will be in equilibrium with that rate of interest and that level of employment. Thus, it was a mistake to speak ofthenatural rate of interest or to suggest that the above definition would yield a unique value for the rate of interest irrespective of the level of employment. . . .If there is any such rate of interest, which is unique and significant, it must be the rate which we might term the

neutralrate of interest, namely, the natural rate in the above sense which is consistent withfullemployment, given the other parameters of the system; though this rate might be better described, perhaps, as theoptimumrate. (pp. 242-43)

Because Keynes believed that an increased in the expected future price level implies an increase in the marginal efficiency of capital, it follows that an increase in expected inflation under conditions of less than full employment would increase investment spending and employment, thereby raising the real rate of interest as well the nominal rate. Cottrell (1994) has attempted to make an argument along such lines within a traditional IS-LM framework. I believe that, in a Fisherian framework, my argument points in a similar direction.