Few people would, I think, take exception to the claim that, in a well-functioning monetary system, the quantity of money supplied should seldom differ, and should never differ very much, from the quantity demanded. What's controversial isn't that claim itself, but the suggestion that it supplies a reason for preferring some path of money supply adjustments over others, or some monetary arrangements over others.
Why the controversy? As we saw in the last installment, the demand for money ultimately consists, not of a demand for any particular number of money units, but of a demand for a particular amount of monetary purchasing power. Whatever amount of purchasing X units of money might accomplish, when the general level of prices given by P, ½X units might accomplish equally well, were the level of prices ½P. It follows that changes in the general level of prices might, in theory at least, serve just as well as changes in the available quantity of money units as a means for keeping the quantity of money supplied in line with the quantity demanded.
But then it follows as well that, if our world is one in which prices are "perfectly flexible," meaning that they always adjust instantly to a level that eliminates any monetary shortage or surplus, any pattern of money supply changes will avoid money supply-demand discrepancies, or "monetary disequilibrium," as well as any other. The goal of avoiding bouts of monetary disequilibrium would in that case supply no grounds for preferring one monetary system or policy over another, or for preferring a stable level of spending over an unstable level. Any such preference would instead have to be justified on other grounds.
So, a decision: we can either adopt the view that prices are indeed perfectly flexible, and proceed to ponder why, despite that view, we might prefer some monetary arrangements to others; or we can subscribe to the view that prices are generally not perfectly flexible, and then proceed to assess alternative monetary arrangements according to their capacity to avoid a non-trivial risk of monetary disequilibrium.
Your guide does not hesitate for a moment to recommend the latter course. For while some prices do indeed appear to be quite flexible, even adjusting almost continually, at least during business hours (prices of goods and financial assets traded on organized exchanges come immediately to mind), in order for the general level of prices to instantly accommodate changes to either the quantity of money supplied or the quantity demanded, it must be the case, not merely that some or many prices are quite flexible, but that all of them are. If, for example, the nominal stock of money were to double arbitrarily and independently of any change in demand, prices would generally have to double in order for equilibrium to be restored. (Recall: twice as many units of money will command the same purchasing power as the original amount only when each unit commands half as much purchasing power as before.) It follows that, so long as any prices are slow to adjust, the price level must be slow to adjust as well. Put another way, an economy's price level is only as flexible as its least flexible prices.
And only a purblind observer can fail to notice that some prices are far from fully flexible. The reason for this isn't hard to grasp: changing prices is sometimes costly; and when it is, sellers have reason to avoid doing it often. Economists use the expression "menu costs" to refer generally to the costs of changing prices, conjuring up thereby the image of a restaurateur paying a printer for a batch of new menus, for the sake of accommodating the rising costs of beef, fish, vegetables, wait staff, cooks, and so forth, or the restaurants' growing popularity, or both. In fact both the restaurants' operating costs and the demand for its output change constantly. Nevertheless it usually wouldn't make sense to have new menus printed every day, let alone several times a day, to reflect all these fluctuations! Electronic menus would help, of course, and now it is easy to conceive of them (though it wasn't not long ago). But those are costly as well, which is why (or one reason why) most restaurants don't use them.
The cost of printing menus is, however, trivial compared to that of changing many other prices. The prices paid for workers, whether wage or salaried, are notoriously difficult to change, except perhaps according to a prearranged schedule, which can't itself accommodate unexpected change. Renegotiating wages or salaries can be an extremely costly business, as well as a time-consuming one.
"Menu costs" can account for prices being sticky even when the nature of underlying changes in supply or demand conditions is well understood. Suppose, for example, that a restaurant's popularity is growing at a steady and known rate. That fact still wouldn't justify having new menus printed every day, or every hour, or perhaps even every week. But add the possibility that a perceived increase in demand may not last, and the restaurateur has that much more reason to delay ordering new menus: after all, if demand subsides again, the new menus may cost more than turning a few customers away would have. (The menus might also annoy customers who would dislike not being able to anticipate what their meal will cost.) Now imagine an employer asking his workers to take a wage rate cut because business was slack last quarter. Get the idea? If not, there's a vast body of writings you can refer to for more examples and evidence.
These days it is common for economists who insist on the "stickiness" of the price level to be referred to, or to refer to themselves, as "New Keynesians." But the label is misleading. Although John Maynard Keynes had plenty of innovative ideas, the idea that prices aren't perfectly flexible wasn't one of them. Instead, by 1936, when Keynes published his General Theory, the idea that prices aren't fully flexible was old-hat: no economists worth his or her salt thought otherwise. The assumption that prices are fully flexible, or "continuously market clearing," is in contrast a relatively recent innovation, having first become prominent in the 1980s with the rise of the "New Classical" school of economists, who subscribe to it, not on empirical grounds, but because they confuse the economists' construct of an all-knowing central auctioneer, who adjusts prices costlessly and continually to their market-clearing levels, with the means by which prices are determined and changed in real economies.
Let New Classical economists ruminate on the challenge of justifying any particular monetary regime in a world of perfectly flexible prices. The rest of us needn't bother. Instead, we can accept the reality of "sticky" prices, and let that reality inform our conclusions concerning which sorts of monetary regimes are more likely, and which ones less likely, to avoid temporary surpluses and shortages of money and their harmful consequences.
What consequences are those? The question is best answered by first recognizing the crucial economic insight that a shortage of money must have as its counterpart a surplus of goods and services and vice versa. When money, the means of exchange, is in short supply, exchange itself, meaning spending of all sorts, suffers, leaving sellers disappointed. In contrast, when money is superabundant, spending grows excessively, depleting inventories and creating shortages. Yet these are only the most obvious consequences of monetary disequilibrium. Other consequences follow from the fact that, owing to different prices' varying degrees of stickiness, the process of moving from a defunct level of equilibrium prices to a new one necessarily involves some temporary distortion of relative price signals, and associated economic waste. A price system has work enough to do in coming to grips with ongoing changes in consumer tastes and technology, among many other non-monetary factors that influence supply and demand for particular goods and services, without also having to reckon with monetary disturbances that call for scaling all prices up or down. The more it must cope with the need to re-scale prices, the less capable it becomes at fine-tuning them to reflect changing conditions within particular markets.
Hyperinflations offer an extreme case in point, for during them sellers often resort to "indexing" local-currency prices to the local currency's exchange rate with respect to some relatively stable foreign currency. That is, they cease referring altogether to the specific conditions in the markets for particular goods, and settle instead for keeping their prices roughly consistent with rapidly changing monetary conditions. In light of this tendency it's hardly surprising that hyperinflations lead to all sorts of waste, if not to the utter collapse of the economies they afflict. If relative prices can become so distorted during hyperinflations as to cease entirely to be meaningful indicators of goods' and services' relative scarcity, it's also true that the usefulness of price signals in promoting the efficient use of scarce resources declines to a more modest extent during less severe bouts of monetary disequilibrium.
What sort of monetary policy or regime best avoids the costs of having too much or too little money? In an earlier post, I've suggested that keeping the supply of money in line with the demand for it, without depending on help in the shape of adjustments to the price level, is mainly a matter of achieving a steady and predictable overall flow of spending. But why spending? Why not maintain a stable price level, or a stable and predictable rate of inflation? If, as I've claimed, changes in the general level of prices are an economy's way of coping, however imperfectly, with monetary shortages and surpluses, then surely an economy in which the price level remains constant, or roughly so, must be one in which such surpluses and shortages aren't occurring. Right?
No, actually. Despite everything I've said here, monetary order, instead of going hand-in-hand with a stable level of prices or rate of inflation, is sometimes best achieved by tolerating price level or inflation rate changes. A paradox? Not really. But as this post is already too long, I must put off explaining why until next time.
 For details see Leland Yeager's essay, "New Keynesians and Old Monetarists," reprinted in The Fluttering Veil.
[Cross-posted from Alt-M.org]