Principles of Economics by Alfred Marshall (1890)

Book Five: General Relations of Demand, Supply and Value

Chapter 2, Temporary Equilibrium of Demand and Supply

1. The simplest case of balance or equilibrium between. desire and effort is found when a person satisfies one of his wants by his own direct work. When a boy picks blackberries for his own eating, the action of picking is probably itself pleasurable for a while; and for some time longer the pleasure of eating is more than enough to repay the trouble of picking. But after he has eaten a good deal, the desire for more diminishes; while the task of picking begins to cause weariness, which may indeed be a feeling of monotony rather than of fatigue. Equilibrium is reached when at last his eagerness to play and his disinclination for the work of picking counterbalance the desire for eating. The satisfaction which he can get from picking fruit has arrived at its maximum: for up to that time every fresh picking has added more to his pleasure than it has taken away; and after that time any further picking would take away from his pleasure more than it would add. (1)

In a casual bargain that one person makes with another, as for instance when two backwoodsmen barter a rifle for a canoe, there is seldom anything that can properly be called an equilibrium of supply and demand: there is probably a margin of satisfaction on either side; for probably the one would be willing to give something besides the rifle for the canoe, if he could not get the canoe otherwise; while the other would in case of necessity give something besides the canoe for the rifle.

It is indeed possible that a true equilibrium may be arrived at under a system of barter; but barter, though earlier in history than buying and selling, is in some ways more intricate; and the simplest cases of a true equilibrium value are found in the markets of a more advanced state of civilization.

We may put aside as of little practical importance a class of dealings which has been much discussed. They relate to pictures by old masters, rare coins and other things, which cannot be "graded" at all. The price at which each is sold, will depend much on whether any rich persons with a fancy for it happen to be present at its sale. If not, it will probably be bought by dealers who reckon on being able to sell it at a profit; and the variations in the price for which the same picture sells at successive auctions, great as they are, would be greater still if it were not for the steadying influence of professional purchasers.

2. Let us then turn to the ordinary dealings of modern life; and take an illustration from a corn-market in a country town, and let us assume for the sake of simplicity that all the corn in the market is of the same quality. The amount which each farmer or other seller offers for sale at any price is governed by his own need for money in hand, and by his calculation of the present and future conditions of the market with which he is connected. There are some prices which no seller would accept, some which no one would refuse. There are other intermediate prices which would be accepted for larger or smaller amounts by many or all of the sellers. Everyone will try to guess the state of the market and to govern his actions accordingly. Let us suppose that in fact there are not more than 600 quarters, the holders of which are willing to accept as low a price as 35s.; but that holders of another hundred would be tempted by 36s.; and holders of yet another three hundred by 37s. Let us suppose also that a price of 37s. would tempt buyers for only 600 quarters; while another hundred could be sold at 36s., and yet another two hundred at 35s. These facts may be put out in a table thus: —

At the price Holders will be Buyer will be

willing to sell willing to buy

37s. 1000 quarters 600 quarters

36s. 700 " 700 "

35s. 600 " 900 "

Of course some of those who are really willing to take 36s. rather than leave the market without selling, will not show at once that they are ready to accept that price. And in like manner buyers will fence, and pretend to be less eager than they really are. So the price may be tossed hither and thither like a shuttlecock, as one side or the other gets the better in the "higgling and bargaining" of the market. But unless they are unequally matched; unless, for instance, one side is very simple or unfortunate in failing to gauge the strength of the other side, the price is likely to be never very far from 36s.; and it is nearly sure to be pretty close to 36s. at the end of the market. For if a holder thinks that the buyers will really be able to get at 36s. all that they care to take at that price, he will be unwilling to let slip past him any offer that is well above that price.

Buyers on their part will make similar calculations; and if at any time the price should rise considerably above 36s. they will argue that the supply will be much greater than the demand at that price: therefore even those of them who would rather pay that price than go unserved, wait; and by waiting they help to bring the price down. On the other hand, when the price is much below 36s., even those sellers who would rather take the price than leave the market with their corn unsold, will argue that at that price the demand will be in excess of the supply: so they will wait, and by waiting help to bring the price up.

The price of 36s. has thus some claim to be called the true equilibrium price: because if it were fixed on at the beginning, and adhered to throughout, it would exactly equate demand and supply (i.e. the amount which buyers were willing to purchase at that price would be just equal to that for which sellers were willing to take that price); and because every dealer who has a perfect knowledge of the circumstances of the market expects that price to be established If he sees the price differing much from 36s. he expects that a change will come before long, and by anticipating it he helps it to come quickly.

It is not indeed necessary for our argument that any dealers should have a thorough knowledge of the circumstances of the market. Many of the buyers may perhaps underrate the willingness of the sellers to sell, with the effect that for some time the price rules at the highest level at which any buyers can be found; and thus 500 quarters may be sold before the price sinks below 37s. But afterwards the price must begin to fall and the result will still probably be that 200 more quarters will be sold, and the market will close on a price of about 36s. For when 700 quarters have been sold, no seller will be anxious to dispose of any more except at a higher price than 36s., and no buyer will be anxious to purchase any more except at a lower price than 36s. In the same way if the sellers had underrated the willingness of the buyers to pay a high price, some of them might begin to sell at the lowest price they would take, rather than have their corn left on their hands, and in this case much corn might be sold at a price of 35s.; but the market would probably close on a price of 36s. and a total sale of 700 quarters. (2)

3. In this illustration there is a latent assumption which is in accordance with the actual conditions of most markets; but which ought to be distinctly recognized in order to prevent its creeping into those cases in which it is not justifiable. We tacitly assumed that the sum which purchasers were willing to pay, and which sellers were willing to take, for the seven hundredth quarter would not be affected by the question whether the earlier bargains had been made at a high or a low rate. We allowed for the diminution in the buyers' need of corn [its marginal utility to them] as the amount bought increased. But we did not allow for any appreciable change in their unwillingness to part with money [its marginal utility]; we assumed that that would be practically the same whether the early payments had been at a high or a low rate.

This assumption is justifiable with regard to most of the market dealings with which we are practically concerned. When a person buys anything for his own consumption, he generally spends on it a small part of his total resources; while when he buys it for the purposes of trade, he looks to re-selling it, and therefore his potential resources are not diminished. In either case there is no appreciable change in his willingness to part with money. There may indeed be individuals of whom this is not true; but there are sure to be present some dealers with large stocks of money at their command; and their influence steadies the market. (3)

The exceptions are rare and unimportant in markets for commodities; but in markets for labour they are frequent and important. When a workman is in fear of hunger, his need of money [its marginal utility to him] is very great; and, if at starting, he gets the worst of the bargaining, and is employed at low wages, it remains great, and he may go on selling his labour at a low rate. That is all the more probable because, while the advantage in bargaining is likely to be pretty well distributed between the two sides of a market for commodities, it is more often on the side of the buyers than on that of the sellers in a market for labour. Another difference between a labour market and a market for commodities arises from the fact that each seller of labour has only one unit of labour to dispose of. These are two among many facts, in which we shall find, as we go on, the explanation of much of that instinctive objection which the working classes have felt to the habit of some economists, particularly those of the employer class, of treating labour simply as a commodity and regarding the labour market as like every other market; whereas in fact the differences between the two cases, though not fundamental from the point of view of theory, are yet clearly marked, and in practice often very important.

The theory of buying and selling becomes therefore much more complex when we take account of the dependence of marginal utility on amount in the case of money as well as of the commodity itself. The practical importance of this consideration is not very great. But a contrast is drawn in Appendix F between barter and dealings in which one side of each exchange is in the form of general purchasing power. In barter a person 's stock of either commodity exchanged needs to be adjusted closely to his individual wants. If his stock is too large he may have no good use for it. If his stock is too small he may have some difficulty in finding any one who can conveniently give him what he wants and is also in need of the particular things of which he himself has a superfluity. But any one who has a stock of general purchasing power, can obtain any thing he wants as soon as he meets with any one who has a superfluity of that thing. he needs not to hunt about till he comes across "the double coincidence" of a person who can spare what he wants, and also wants what he can spare. Consequently every one, and especially a professional dealer, can afford to keep command over a large stock of money; and can therefore make considerable purchases without depleting his stock of money or greatly altering its marginal value.


1. See IV, I, section 2, and Note XII in the Mathematical Appendix.

2. A simple form of the influence which opinion exerts on the action of dealers, and therefore on market price, is indicated in this illustration: we shall be much occupied with more complex developments of it later on.

3. For instance a buyer is sometimes straitened for want of ready money, and has to let offers pass by him in no way inferior to others which he has gladly accepted: his own funds being exhausted, he could not perhaps borrow except on terms that would take away all the profit that the bargains had at first sight offered. But if the bargain is really a good one, some one else, who is not so straitened, is nearly sure to get hold of it.

Again, it is possible that several of those who had been counted as ready to sell corn at a price of 36s. were willing to sell only because they were in urgent need of a certain amount of ready money; if they succeeded in selling some corn at a high price, there might be a perceptible diminution in the marginal utility of ready money to them; and therefore they might refuse to sell for 36s. a quarter all the corn which they would have sold if the price had been 36s. throughout.

In this case the sellers in consequence of getting an advantage in bargaining at the beginning of the market might retain to the end a price higher than the equilibrium price. The price at which the market dosed would be an equilibrium price; and though not properly described as the equilibrium price, it would be very unlikely to diverge widely from that price.

Conversely, if the market had opened much to the disadvantage of the sellers and they had sold some corn very cheap, so that they remained in great want of ready money, the final utility of money to them might have remained so high that they would have gone on selling considerably below 36s. until the buyers had been supplied with all that they cared to take. The market would then close without the true equilibrium price having ever been reached, but a very near approach would have been made to it.

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