This is going to be my third consecutive post about Scott Sumner (well, not only about Scott), and we seem to be arguing about something, but it may not be exactly clear what the argument is about. Some people, based on comments on this and other blogs, apparently think that I am defending the Keynesian model against Scott’s attacks. Others even accuse me of advocating – horrors! – tax and spend policies as the way to stimulate the economy. In fact, Scott himself seems to think that what I am trying to do is defend what he calls the hydraulic Keynesian model. That’s a misunderstanding; I am simply trying to enforce some basic standards of good grammar in arguing about economic models, in this case the hydraulic Keynesian model. I am not a fan of the hydraulic Keynesian model, but most economists, even anti-Keynesians like Hayek (see here), have acknowledged that in a severe recession or depression, when there is substantial unemployment of nearly all factors of production, the model does provide some insight. I have also explained (here and here) that it is possible to translate the simple Keynesian model of a depression and a liquidity trap into the language of the supply of and demand for money. So at some level of generality, the propositions of the Keynesian model can be treated as fairly trivial and non-controversial.
So what do I mean when I say that I am just trying to enforce basic standards of good grammar? I mean that good grammar is not about what you choose to say; it is about how you say it. Using good grammar doesn’t prevent you from saying anything you want to; it just prevents you from saying it in certain not very comprehensible ways. If you use good grammar, you enhance your chances of saying what you want to say coherently and avoiding needless confusion. Sure some grammatical rules are purely conventional or nitpicks, but good writers and speakers know which grammatical rules can be safely ignored and which can’t. Using bad grammar leads you make statements that are confusing or ambiguous or otherwise incoherent even though the point that you are trying to make may be perfectly clear to you. Making the point clear to someone else requires you to follow certain semantic rules that help others to follow what you are saying. It is also possible that when you make an ungrammatical statement, you are disguising (and at the same time revealing) some confusion that you yourself may not be aware of, and had you made the statement grammatically you might have become aware that you had not fully thought through what you were trying to say. So in a discussion about the Keynesian model, I regard myself as a neutral observer; I don’t care if you are making a statement for or against the model. But I want you to make the statement grammatically.
That’s right; my problem with Scott is that he is using bad grammar. When Scott says he can derive a substantive result about the magnitude of the balanced-budget multiplier from an accounting identity between savings and investment, he is making a theoretically ungrammatical statement. My problem is not with whatever value he wants to assign to the balanced-budget multiplier. My problem is that he thinks that he can draw any empirically meaningful conclusion — about anything — from an accounting identity. Scott defends himself by citing Mankiw and Krugman and others who assert that savings and investment are identically equal. I don’t have a copy of any of Krugman’s textbooks, so I don’t know what he says about savings and investment being identically equal, but I was able to find the statement in Mankiw’s text. And yes, he does say it, and he was speaking incoherently when he said it. Now, it is one thing to make a nonsense statement, which Mankiw obviously did, and it is another to use it as a step – in fact a critical step — in a logical proof, which is what Scott did.
The unfortunate fact is that the vast majority of economics textbooks starting with Samuelson’s classic text (though not until the fourth edition) have been infected by this identity virus, even including the greatest economics textbook ever written. The virus was introduced into economics by none other than Keynes himself in his General Theory. He was properly chastised for doing so by Robertson, Hawtrey, Haberler, and Lutz among others. Perhaps because the identity between savings and investment in the national income accounts reinforced the misunderstanding and misconception that the Keynesian model is somehow based on an accounting identity between investment and savings, the virus withstood apparently conclusive refutation and has clearly become highly entrenched as a feature of the Keynesian model.
The confusion was exacerbated because, in the most common form of the Keynesian model, the timeless, lagless form with the instantaneous multiplier, the model has meaning only in equilibrium for which the equality of savings and investment is a necessary and sufficient condition. This misunderstanding has led to completely illegitimate attempts to identify points on the Keynesian cross diagram away from the point of intersection as disequilibria characterized by a difference between planned (ex ante) and realized (ex post) savings or planned and realized investment. It is legitimate to refer to the equality of savings and investment in equilibrium, but you can’t extrapolate from a change in one or the other to determine how the equilibrium changes as a result of the specified change in savings or investment, which is what Scott tried to do. So, yes, the mistaken identification of savings and investment is distressingly widespread, but unfortunately Scott has compounded the confusion, taking it to an even higher level. Let me again cite as the key source identifying and tracking down all the confusions and misconceptions associated with treating savings and investment (or expenditure and income) as identically equal the classic paper by Richard Lipsey, “The Foundations of the Theory of National Income,” originally published in 1972 in Essays in Honour of Lord Robbins and reprinted in Lipsey Macroeconomic Theory and Policy: The Selected Essays of Richard G. Lipsey, vol. 2.
That’s all for now. I still need to respond to some of Scott’s arguments in detail, clear up a mistake in my previous post and say some more about the savings is identically equal to investment virus.