Substitution and Allometry

Brad DeLong channels Milton Friedman:

Supply and demand curves are never horizontal. They are never vertical. If somebody says that quantities change without changing prices, or that prices change without changing quantities, hold tightly onto your wallet–there is something funny going on.

Yes, this is how economists think, or at least think they think. And there’s more than a bit of truth in it. Certainly in the case at hand, DeLong-cum-Friedman is right, and Myron Scholes is wrong: It’s neither plausible nor properly thinking like an economist to suppose that if unconventional monetary policy can substantially reduce the quantity of risky financial assets held by the public, the price of such assets — the relevant interest rates — will remain unchanged.

That’s right. But it’s not the only way to be right.

Consider the marginal propensity to consume, that workhorse of practical macroeconomic analysis. It’s impossible to talk about the effects of changes in government spending or other demand-side shifts without it. What it says is that, in the short run at least there is a regular relationship between the level of income and the proportion of income spent on current consumption, both across households and over time. Now, of course, you can explain this relationship with a story about relative prices driving substitution between consumption now and consumption later, if you want. But this story is just tacked on, you don’t need it to observe the empirical relationship and make predictions accordingly. And more restrictive versions of the substitution story, like the permanent income hypothesis, while they do add some positive content, tend not to survive confrontations with the data. The essential point is that whatever one thinks are the underlying social or psychological processes driving consumption decisions (it’s unlikely they can be usefully described as maximizing anything) we reliably observe that when income rises, less of it goes to consumption; when it falls, more of it does.

In biology, a regular relationship between the size of an organism and the proportions of its body is called an allometry. A classic example is the skeleton of mammals, which becomes much more robust and massive relative to the size of the body as the body size increases. Economists are fond of importing concepts from harder sciences, so why not this one? After all, consumption is just one of a number of areas where we rely on stable relations between changes in aggregates and relative changes in their components. There’s fixed-coefficient production functions (strictly, an isometry rather than allometry, but we can use the term more broadly than biologists do); the stylized fact, important to (inter alia) classical Marxists, that capital-output ratios rise as output grows; or composition effects in trade, which seem to play such a major role in explaining the collapse in trade volumes during the Great Recession.

This is a way of thinking about economic shifts that doesn’t require the price-quantity links that Friedman-DeLong think are the mark of honest economics, even if you can come up with some price-signal based microfoundation for any observed allometry. It’s more the spirit of the old institutionalists, or traditional development or industrial-organization economics, which tend to take a natural historian’s view of the economy. Of course, not every change in proportion can be explained in terms of regular responses to a change in the aggregate they’re part of. Plenty of times, we should still think in terms of prices and substitution; the hard question is exactly when. But it would be an easier question to answer, if we were clearer about the alternatives.

What is Keynesianism?

[A bit of thumbsucking inspired by discussion here.]

As a policy of countercyclical demand management, Keynesianism is based on the idea that there are no automatic forces in industrial capitalism that reliably equilibrate aggregate supply and aggregate demand. In the absence of government stabilization policies, the economy will waver between inflationary periods of excess demand and depressed periods of inadequate demand. The main explanation for this instability is that private investment depends on long-term profitability expectations, but since aspects of the future relevant to profitability are fundamentally uncertain [1], these expectations are unanchored and conventional, inevitably subject to large collective shifts independent of current “fundamentals”. Government spending can stabilize demand if G+I varies less over the business cycle than I alone does. For which it’s sufficient that government spending be large. It’s even better if G and I move in opposite directions, but the reason Minsky answered No to Can “It” Happen Again? was because of big government as such, not countercyclical fiscal policy.The focus on cyclical stabilization assumes that there is no systematic long-term divergence between aggregate supply and aggregate demand. But Keynes believed that there was a secular tendency toward stagnation in advanced capitalist economies, so that maintaining full employment meant not just using public expenditure to stabilize private investment demand, but to incrementally replace it. Another way of looking at this is that the steady shift from small-scale to industrial production implies a growing weight of illiquid assets in the form of fixed capital. [2] There is not, however, any corresponding long-term increase in the demand of illiquid liabilities. If anything, the sociological patterns of capitalism point the other way, as industrial dynasties whose social existence was linked to particular enterprises have been steadily replaced by rentiers. [3] The whole line of financial innovations from the first joint-stock companies to the recent securitization boom have been attempts to bridge this gap. But this requires ever-deepening financialization, with all the social waste and instability that implies. It’s the government’s ability to issue liabilities backed by the whole economic output that makes it uniquely able to satisfy the demands of wealth-holders for liquid assets. In the functional finance tradition going back to Lerner, modern states do not possess a budget constraint in the same way households or firms do. Public borrowing has nothing to do with “funding” spending, it’s all about how much government debt the authorities want the banking system to hold. If the demand for safe, liquid assets rises secularly over time, so should government borrowing.From this point of view, one important source of the recent financial crisis was the surpluses of the 1990s, and insufficient borrowing by the US government in general. By restricting the supply of Treasuries, this excessive fiscal restraint spurred the creation of private sector substitutes purporting to offer similar liquidity properties, in the form of various asset-backed securities. (Here is a respectable mainstream guy making essentially this argument. [4]) But these new financial assets remained at bottom claims on specific illiquid real assets and their liquidity remained vulnerable to shifts in (expectations of) the value of those assets. The response to the crisis in 2008 then consists of the Fed retroactively correcting the undersupply of government liabilities by engaging in a wholesale swap of public for private liabilities, leaving banks (and liquidity-demanding wealth owners) holding government liabilities instead of private financial assets. The increase in public debt wasn’t an unfortunate side-effect of the solution to the financial crisis, it was the solution. Along the same lines, I sometimes wonder how much the huge proportion of government debt on bank balance sheets — 75 percent of assets in 1945 vs. 1.5 percent in 2005)contributed to the financial stability of the immediate postwar era. With that many safe assets sloshing around, it didn’t take financial engineering or speculative bubbles to convince banks to hold claims on fixed capital and housing. But as the supply of government debt has dwindled the inducements to hold other assets have had to grow increasingly garish. From which I conclude that ever-increasing government deficits may in fact be better Keynesianism – theoretically, historically and pragmatically – than countercyclical demand management.
[1] Davidson, Shackle, etc. would say nonergodic. This strand of Post Keynesian thinking often wanders beyond my comfort zone.[2] This shift is ongoing, not just historical — not only do capital-output ratios continue to rise in manufacturing, but we’re seeing the “industrialization” of retail, health care, etc.

[3] Schumpeter is the only major economist to give sufficient attention to the sociology of the capitalist class, IMO. Marx’s insistence that the capitalist is simply the human representative of capital is a powerful analytic tool for many purposes, but it leaves some important questions unasked.

[4] Here is another.

Stein’s law modified

Krugman cites it: If something can’t go on forever, it will stop. True.

Also true:

Even if something can go on forever, it will stop eventually.
Even if something can’t go on forever, it can go on for a very long time.

One might say the difference between these corollaries and Stein’s original is the difference between a real-world, historical approach to macro and the equilibrium approach of the mainstream. Fresh or salty, it’s all water “when the storm is past and the ocean is flat again…”