In this selection from John Stuart Mill's, Principles of Political Economy, Mill discusses the possibility that there may not be enough demand to purchase the commodities that an economy produces.
He begins by discussing the purely technical question of whether there may be more commodities than people have money to buy, and he shows this is impossible; economists still see this point today. Then he discusses the more interesting question of whether there may be more commodities than people have the desire to buy, and he shows this is impossible because workers would shorten their hours; economists have forgotten this basic principle of classical economics.
When these writers speak of the supply of commodities as outrunning the demand, it is not clear which of the two elements of demand they have in view—the desire to possess, or the means of purchase; whether their meaning is that there are, in such cases, more consumable products in existence than the public desires to consume, or merely more than it is able to pay for. In this uncertainty, it is necessary to examine both suppositions.
First, let us suppose that the quantity of commodities produced is not greater than the community would be glad to consume: is it, in that case, possible that there should be a deficiency of demand for all commodities for want of the means of payment? Those who think so cannot have considered what it is which constitutes the means of payment for commodities. It is simply commodities. Each person's means of paying for the productions of other people consists of those which he himself possesses. All sellers are inevitably and ex vi termini buyers. Could we suddenly double the productive powers of the country, we should double the supply of commodities in every market; but we should, by the same stroke, double the purchasing power. Everybody would bring a double demand as well as supply: everybody would be able to buy twice as much, because every one would have twice as much to offer in exchange. It is probable, indeed, that there would now be a superfluity of certain things. Although the community would willingly double its aggregate consumption, it may already have as much as it desires of some commodities, and it may prefer to do more than double its consumption of others, or to exercise its increased purchasing power on some new thing. If so, the supply will adapt itself accordingly, and the values of things will continue to conform to their cost of production. At any rate, it is a sheer absurdity that all things should fall in value, and that all producers should, in consequence, be insufficiently remunerated. If values remain the same, what becomes of prices is immaterial, since the remuneration of producers does not depend on how much money, but on how much of consumable articles, they obtain for their goods. Besides, money is a commodity; and if all commodities are supposed to be doubled in quantity, we must suppose money to be doubled too, and then prices would no more fall than values would.
A general over-supply, or excess of all commodities above the demand, so far as demand consists in means of payment, is thus shown to be an impossibility. But it may perhaps be supposed that it is not the ability to purchase, but the desire to possess, that falls short, and that the general produce of industry may be greater than the community desires to consume—the part, at least, of the community which has an equivalent to give. It is evident enough that produce makes a market for produce, and that there is wealth in the country with which to purchase all the wealth in the country; but those who have the means may not have the wants, and those who have the wants may be without the means. A portion, therefore, of the commodities produced may be unable to find a market from the absence of means in those who have the desire to consume, and the want of desire in those who have the means.
This is much the most plausible form of the doctrine, and does not, like that which we first examined, involve a contradiction. There may easily be a greater quantity of any particular commodity than is desired by those who have the ability to purchase, and it is abstractedly conceivable that this might be the case with all commodities. The error is in not perceiving that though all who have an equivalent to give might be fully provided with every consumable article which they desire, the fact that they go on adding to the production proves that this is not actually the case.
Assume the most favourable hypothesis for the purpose, that of a limited community, every member of which possesses as much of necessaries and of all known luxuries as he desires: and since it is not conceivable that persons whose wants were completely satisfied would labour and economize to obtain what they did not desire, suppose that a foreigner arrives and produces an additional quantity of something of which there was already enough. Here, it will be said, is over-production: true, I reply; over-production of that particular article: the community wanted no more of that, but it wanted something. The old inhabitants, indeed, wanted nothing; but did not the foreigner himself want something? When he produced the superfluous article, was he labouring without a motive? He has produced, but the wrong thing instead of the right. He wanted, perhaps, food, and has produced watches, with which everybody was sufficiently supplied. The new comer brought with him into the country a demand for commodities, equal to all that he could produce by his industry, and it was his business to see that the supply he brought should be suitable to that demand. If he could not produce something capable of exciting a new want or desire in the community, for the satisfaction of which some one would grow more food and give it to him in exchange, he had the alternative of growing food for himself; either on fresh land, if there was any unoccupied, or as a tenant, or partner, or servant, of some former occupier, willing to be partially relieved from labour. He has produced a thing not wanted, instead of what was wanted; and he himself, perhaps, is not the kind of producer who is wanted; but there is no over-production; production is not excessive, but merely ill assorted.
We saw before, that whoever brings additional commodities to the market, brings an additional power of purchase; we now see that he brings also an additional desire to consume; since if he had not that desire, he would not have troubled himself to produce. Neither of the elements of demand, therefore, can be wanting, when there is an additional supply; though it is perfectly possible that the demand may be for one thing, and the supply may unfortunately consist of another.
John Stuart Mill, Principles of Political Economy with some of their Applications to Social Philosophy, Book III, Chapter 14, sections 5-8.
Though the question was purely theoretical when Mill wrote, because wages were near the subsistence level, Mill assumes that workers can choose their hours because they are freely contracting agenst serving their own economic purposes.
This assumption is necessary to market economic theory. Just as individuals must be able to choose freely between one commodity and another to optimize the output of individual commodities, people must be able to choose freely between commodities and leisure to optimize the output of commodities in general.
Today, our economy grows irrationally, beyond the amount that would maximize people's satisfaction, because workers do not have the right to choose their hours. In order to avoid unemployment, we must stimulate economic growth to provide every worker with a standard 40-hour job, even if many workers would prefer more free time over more commodities. With choice of worker hours, we could produce as much as workers actually want.