Against Say's Law--which (most of the time at least) Say did not strictly believe...
John Stuart Mill (1844):
In order to afford the explanations, with which it is necessary to take the doctrine of the impossibility of an excess of all commodities, we must advert for a moment to the argument by which this impossibility is commonly maintained. There can never, it is said, be a want of buyers for all commodities; because whoever offers a commodity for sale, desires to obtain a commodity in exchange for it, and is therefore a buyer by the mere fact of his being a seller. The sellers and the buyers, for all commodities taken together, must, by the metaphysical necessity of the case, be an exact equipoise to each other; and if there be more sellers than buyers of one thing, there must be more buyers than sellers for another. This argument is evidently founded on the supposition of a state of barter; and, on that supposition, it is perfectly incontestable. When two persons perform an act of barter, each of them is at once a seller and a buyer. He cannot sell without buying. Unless he chooses to buy some other person's commodity, he does not sell his own.
If, however, we suppose that money is used, these propositions cease to be exactly true. It must be admitted that no person desires money for its own sake, (unless some very rare cases of misers be an exception,) and that he who sells his commodity, receiving money in exchange, does so with the intention of buying with that same money some other commodity. Interchange by means of money is therefore, as has been often observed, ultimately nothing but barter. But there is this difference—that in the case of barter, the selling and the buying are simultaneously confounded in one operation; you sell what you have, and buy what you want, by one indivisible act, and you cannot do the one without doing the other. Now the effect of the employment of money, and even the utility of it, is, that it enables this one act of interchange to be divided into two separate acts or operations; one of which may be performed now, and the other a year hence, or whenever it shall be most convenient. Although he who sells, really sells only to buy, he needs not buy at the same moment when he sells; and he does not therefore necessarily add to the immediate demand for one commodity when he adds to the supply of another. The buying and selling being now separated, it may very well occur, that there may be, at some given time, a very general inclination to sell with as little delay as possible, accompanied with an equally general inclination to defer all purchases as long as possible. This is always actually the case, in those periods which are described as periods of general excess. And no one, after sufficient explanation, will contest the possibility of general excess, in this sense of the word. The state of things which we have just described, and which is of no uncommon occurrence, amounts to it. For when there is a general anxiety to sell, and a general disinclination to buy, commodities of all kinds remain for a long time unsold, and those which find an immediate market, do so at a very low price. If it be said that when all commodities fall in price, the fall is of no consequence, since mere money price is not material while the relative value of all commodities remains the same, we answer that this would be true if the low prices were to last for ever. But as it is certain that prices will rise again sooner or later, the person who is obliged by necessity to sell his commodity at a low money price is really a sufferer, the money he receives sinking shortly to its ordinary value. Every person, therefore, delays selling if he can, keeping his capital unproductive in the mean time, and sustaining the consequent loss of interest. There is stagnation to those who are not obliged to sell, and distress to those who are.
It is true that this state can be only temporary, and must even be succeeded by a reaction of corresponding violence, since those who have sold without buying will certainly buy at last, and there will then be more buyers than sellers. But although the general over-supply is of necessity only temporary, this is no more than may be said of every partial over-supply. An overstocked state of the market is always temporary, and is generally followed by a more than common briskness of demand. In order to render the argument for the impossibility of an excess of all commodities applicable to the case in which a circulating medium is employed, money must itself be considered as a commodity. It must, undoubtedly, be admitted that there cannot be an excess of all other commodities, and an excess of money at the same time. But those who have, at periods such as we have described, affirmed that there was an excess of all commodities, never pretended that money was one of these commodities; they held that there was not an excess, but a deficiency of the circulating medium. What they called a general superabundance, was not a superabundance of commodities relatively to commodities, but a superabundance of all commodities relatively to money. What it amounted to was, that persons in general, at that particular time, from a general expectation of being called upon to meet sudden demands, liked better to possess money than any other commodity. Money, consequently, was in request, and all other commodities were in comparative disrepute. In extreme cases, money is collected in masses, and hoarded; in the milder cases, people merely defer parting with their money, or coming under any new engagements to part with it. But the result is, that all commodities fall in price, or become unsaleable. When this happens to one single commodity, there is said to be a superabundance of that commodity; and if that be a proper expression, there would seem to be in the nature of the case no particular impropriety in saying that there is a superabundance of all or most commodities, when all or most of them are in this same predicament.