# Principles of Political Economy (J.S. Mill, 1871), vol. 1/Book III, Chapter II

CHAPTER II.
OF DEMAND AND SUPPLY, IN THEIR RELATION TO VALUE.
§ 1.That a thing may have any value in exchange, two conditions are necessary. It must be of some use; that is (as already explained) it must conduce to some purpose, satisfy some desire. No one will pay a price, or part with anything which serves some of his purposes, to obtain a thing which serves none of them. But, secondly, the thing must not only have some utility, there must also be some difficulty in its attainment. "Any article whatever," says Mr. De Quincey, "to obtain that artificial sort of value which is meant by exchange value, must begin by offering itself as a means to some desirable purpose; and secondly, even though possessing incontestably this preliminary advantage, it will never ascend to an exchange value in cases where it can be obtained gratuitously and without effort; of which last terms both are necessary as limitations. For often it will happen that some desirable object may be obtained gratuitously; stoop, and you gather it at your feet; but still, because the continued iteration of this stooping exacts a laborious effort, very soon it is found, that to gather for yourself virtually is not gratuitous. In the vast forests of the Canadas, at intervals, wild strawberries may be gratuitously gathered by shiploads: yet such is the exhaustion of a stooping posture, and of a labour so monotonous, that everybody is soon glad to resign the service into mercenary hands."
As was pointed out in the last chapter, the utility of a thing in the estimation of the purchaser, is the extreme limit ​of its exchange value: higher the value cannot ascend; peculiar circumstances are required to raise it so high. This topic is happily illustrated by Mr. De Quincey. "Walk into almost any possible shop, buy the first article you see; what will determine its price? In the ninety-nine cases out of a hundred, simply the element D—difficulty of attainment. The other element U, or intrinsic utility, will be perfectly in-operative. Let the thing (measured by its uses) be, for your purposes, worth ten guineas, so that you would rather give ten guineas than lose it; yet, if the difficulty of producing it be only worth one guinea, one guinea is the price which it will bear. But still not the less, though U is inoperative, can U be supposed absent? By no possibility; for, if it had been absent, assuredly you would not have bought the article even at the lowest price. U acts upon you, though it does not act upon the price. On the other hand, in the hundredth case, we will suppose the circumstances reversed: you are on Lake Superior in a steam-boat, making your way to an unsettled region 800 miles a-head of civilization, and consciously with no chance at all of purchasing any luxury whatsoever, little luxury or big luxury, for the space of ten years to come. One fellow-passenger, whom you will part with before sunset, has a powerful musical snuff-box; knowing by experience the power of such a toy over your own feelings, the magic with which at times it lulls your agitations of mind, you are vehemently desirous to purchase it. In the hour of leaving London you had forgot to do so; here is a final chance. But the owner, aware of your situation not less than yourself, is determined to operate by a strain pushed to the very uttermost upon U, upon the intrinsic worth of the article in your individual estimate for your individual purposes. He will not hear of D as any controlling power or mitigating agency in the case; and finally, although at six guineas a-piece in London or Paris you might have loaded a waggon with such boxes, you pay sixty rather than lose it when the last knell of the clock has sounded, which summons ​you to buy now or to forfeit for ever. Here, as before, only one element is operative; before it was D, now it is U. But after all, D was not absent, though inoperative. The inertness of D allowed U to put forth its total effect. The practical compression of D being withdrawn, U springs up like water in a pump when released from the pressure of air. Yet still that D was present to your thoughts, though the price was otherwise regulated, is evident; both because U and D must coexist in order to found any case of exchange value whatever, and because undeniably you take into very particular consideration this D, the extreme difficulty of attainment (which here is the greatest possible, viz. an impossibility) before you consent to have the price racked up to U. The special D has vanished; but it is replaced in your thoughts by an unlimited D. Undoubtedly you have submitted to U in extremity as the regulating force of the price; but it was under a sense of D's latent presence. Yet D is so far from exerting any positive force, that the retirement of D from all agency whatever on the price this it is which creates as it were a perfect vacuum, and through that vacuum U rushes up to its highest and ultimate gradation."
This case, in which the value is wholly regulated by the necessities or desires of the purchaser, is the case of strict and absolute monopoly; in which, the article desired being only obtainable from one person, he can exact any equivalent, short of the point at which no purchaser could be found. But it is not a necessary consequence, even of complete monopoly, that the value should be forced up to this ultimate limit; as will be seen when we have considered the law of value in so far as depending on the other element, difficulty of attainment.
§ 2.The difficulty of attainment which determines value, is not always the same kind of difficulty. It sometimes consists in an absolute limitation of the supply. There ​are things of which it is physically impossible to increase the quantity beyond certain narrow limits. Such are those wines which can be grown only in peculiar circumstances of soil, climate, and exposure. Such also are ancient sculptures; pictures by old masters; rare books or coins, or other articles of antiquarian curiosity. Among such may also be reckoned houses and building-ground, in a town of definite extent (such as Venice, or any fortified town where fortifications are necessary to security); the most desirable sites in any town whatever; houses and parks peculiarly favoured by natural beauty, in places where that advantage is uncommon. Potentially, all land whatever is a commodity of this class; and might be practically so, in countries fully occupied and cultivated.
But there is another category (embracing the majority of all things that are bought and sold), in which the obstacle to attainment consists only in the labour and expense requisite to produce the commodity. Without a certain labour and expense it cannot be had: but when any one is willing to incur these, there needs be no limit to the multiplication of the product. If there were labourers enough and machinery enough, cottons, woollens, or linens might be produced by thousands of yards for every single yard now manufactured. There would be a point, no doubt, where further increase would be stopped by the incapacity of the earth to afford more of the material. But there is no need, for any purpose of political economy, to contemplate a time when this ideal limit could become a practical one.
There is a third case, intermediate between the two preceding, and rather more complex, which I shall at present merely indicate, but the importance of which in political economy is extremely great. There are commodities which can be multiplied to an indefinite extent by labour and expenditure, but not by a fixed amount of labour and expenditure. Only a limited quantity can be produced at a given cost: if more is wanted, it must be produced at a greater ​cost. To this class, as has been often repeated, agricultural produce belongs; and generally all the rude produce of the earth; and this peculiarity is a source of very important consequences; one of which is the necessity of a limit to population; and another, the payment of rent.
§ 3.These being the three classes, in one or other of which all things that are bought and sold must take their place, we shall consider them in their order. And first, of things absolutely limited in quantity, such as ancient sculptures or pictures.
Of such things it is commonly said, that their value depends upon their scarcity: but the expression is not sufficiently definite to serve our purpose. Others say, with somewhat greater precision, that the value depends on the demand and the supply. But even this statement requires much explanation, to make it a clear exponent of the relation between the value of a thing, and the causes of which that value is an effect.
The supply of a commodity is an intelligible expression: it means the quantity offered for sale; the quantity that is to be had, at a given time and place, by those who wish to purchase it. But what is meant by the demand? Not the mere desire for the commodity. A beggar may desire a diamond; but his desire, however great, will have no influence on the price. Writers have therefore given a more limited sense to demand, and have defined it, the wish to possess, combined with the power of purchasing. To distinguish demand in this technical sense, from the demand which is synonymous with desire, they call the former effectual demand. After this explanation, it is usually supposed that ​there remains no further difficulty, and that the value depends upon the ratio between the effectual demand, as thus defined, and the supply.
These phrases, however, fail to satisfy any one who requires clear ideas, and a perfectly precise expression of them. Some confusion must always attach to a phrase so inappropriate as that of a ratio between two things not of the same denomination. What ratio can there be between a quantity and a desire, or even a desire combined with a power? A ratio between demand and supply is only intelligible if by demand we mean the quantity demanded, and if the ratio intended is that between the quantity demanded and the quantity supplied. But again, the quantity demanded is not a fixed quantity, even at the same time and place; it varies according to the value; if the thing is cheap, there is usually a demand for more of it than when it is dear. The demand, therefore, partly depends on the value. But it was before laid down that the value depends on the demand. From this contradiction how shall we extricate ourselves? How solve the paradox, of two things, each depending upon the other?
Though the solution of these difficulties is obvious enough, the difficulties themselves are not fanciful; and I bring them forward thus prominently, because I am certain that they obscurely haunt every inquirer into the subject who has not openly faced and distinctly realized them. Undoubtedly the true solution must have been frequently given, though I cannot call to mind any one who had given it before myself, except the eminently clear thinker and skilful expositor, J.B. Say. I should have imagined, however, that it must be familiar to all political economists, if the writings of several did not give evidence of some want of clearness on the point, and if the instance of Mr. De Quincey did not prove that the complete non-recognition and implied denial of it are compatible with great intellectual ingenuity, and close intimacy with the subject matter.
§ 4.Meaning, by the word demand, the quantity demanded, and remembering that this is not a fixed quantity, but in general varies according to the value, let us suppose that the demand at some particular time exceeds the supply, that is, there are persons ready to buy, at the market value, a greater quantity than is offered for sale. Competition takes place on the side of the buyers, and the value rises: but how much? In the ratio (some may suppose) of the deficiency: if the demand exceeds the supply by one-third, the value rises one-third. By no means: for when the value has risen one-third, the demand may still exceed the supply; there may, even at that higher value, be a greater quantity wanted than is to be had; and the competition of buyers may still continue. If the article is a necessary of life, which, rather than resign, people are willing to pay for at any price, a deficiency of one-third may raise the price to double, triple, or quadruple. Or, on the contrary, the competition may cease before the value has risen in even the proportion of the deficiency. A rise, short of one-third, may place the article beyond the means, or beyond the inclinations, of purchasers to the full amount. At what point, then, will the rise be arrested? At the point, whatever it be, which equalizes the demand and the supply: at the price which cuts off the extra third from the demand, or brings forward additional sellers sufficient to supply it. When, in either of these ways, or by a combination of both, the demand becomes equal and no more than equal to the supply, the rise of value will stop.
The converse case is equally simple. Instead of a demand beyond the supply, let us suppose a supply exceeding the ​demand. The competition will now be on the side of the sellers: the extra quantity can only find a market by calling forth an additional demand equal to itself. This is accomplished by means of cheapness; the value falls, and brings the article within the reach of more numerous customers, or induces those who were already consumers to make increased purchases. The fall of value required to re-establish equality, is different in different cases. The kinds of things in which it is commonly greatest are at the two extremities of the scale; absolute necessaries, or those peculiar luxuries, the taste for which is confined to a small class. In the case of food, as those who have already enough do not require more on account of its cheapness, but rather expend in other things what they save in food, the increased consumption occasioned by cheapness, carries off, as experience shows, only a small part of the extra supply caused by an abundant harvest; and the fall is practically arrested only when the farmers withdraw their corn, and hold it back in hopes of a higher price; or by the operations of speculators who buy corn when it is cheap, and store it up to be brought out when more urgently wanted. Whether the demand and supply are equalized by an increased demand, the result of cheapness, or by withdrawing a part of the supply, equalized they are in either case.
Thus we see that the idea of a ratio, as between demand and supply, is out of place, and has no concern in the matter: the proper mathematical analogy is that of an equation. Demand and supply, the quantity demanded and the quantity supplied, will be made equal. If unequal at any moment, competition equalizes them, and the manner in which this is done is by an adjustment of the value. If the demand increases, the value rises; if the demand diminishes, the value falls: again, if the supply falls off, the value rises; and falls if the supply is increased. The rise or the fall continues ​until the demand and supply are again equal to one another: and the value which a commodity will bring in any market, is no other than the value which, in that market, gives a demand just sufficient to carry off the existing or expected supply.
This, then, is the Law of Value, with respect to all commodities not susceptible of being multiplied at pleasure. Such commodities, no doubt, are exceptions. There is another law for that much larger class of things, which admit of indefinite multiplication. But it is not the less necessary to conceive distinctly and grasp firmly the theory of this exceptional case. In the first place, it will be found to be of great assistance in rendering the more common case intelligible. And in the next place, the principle of the exception stretches wider, and embraces more cases, than might at first be supposed.
§ 5.There are but few commodities which are naturally and necessarily limited in supply. But any commodity whatever may be artificially so. Any commodity may be the subject of a monopoly: like tea, in this country, up to 1834; tobacco in France, opium in British India, at present. The price of a monopolized commodity is commonly supposed to be arbitrary; depending on the will of the monopolist, and limited only (as in Mr. De Quincey's case of the musical box in the wilds of America) by the buyer's extreme estimate of its worth to himself. This is in one sense true, but forms no exception, nevertheless, to the dependence of the value on supply and demand. The monopolist can fix the value as high as he pleases, short of what the consumer either could not or would not pay; but he can only do so by limiting the supply. The Dutch East India Company obtained a monopoly price for the produce of the Spice Islands, but to do so they were obliged, in good seasons, to destroy a portion of the crop. Had they persisted in selling all that they produced, they must have forced a ​market by reducing the price, so low, perhaps, that they would have received for the larger quantity a less total return than for the smaller: at least they showed that such was their opinion by destroying the surplus. Even on Lake Superior, Mr. De Quincey's huckster could not have sold his box for sixty guineas, if he had possessed two musical boxes and desired to sell them both. Supposing the cost price of each to be six guineas, he would have taken seventy for the two in preference to sixty for one; that is, although his monopoly was the closest possible, he would have sold the boxes at thirty-five guineas each, notwithstanding that sixty was not beyond the buyer's estimate of the article for his purposes. Monopoly value, therefore, does not depend on any peculiar principle, but is a mere variety of the ordinary case of demand and supply.
Again, though there are few commodities which are at all times and for ever unsusceptible of increase of supply, any commodity whatever may be temporarily so; and with some commodities this is habitually the case. Agricultural produce, for example, cannot be increased in quantity before the next harvest; the quantity of corn already existing in the world, is all that can be had for sometimes a year to come. During that interval, corn is practically assimilated to things of which the quantity cannot be increased. In the case of most commodities, it requires a certain time to increase their quantity; and if the demand increases, then until a corresponding supply can be brought forward, that is, until the supply can accommodate itself to the demand, the value will so rise as to accommodate the demand to the supply.
There is another case, the exact converse of this. There are some articles of which the supply may be indefinitely increased, but cannot be rapidly diminished. There are things so durable that the quantity in existence is at all times very great in comparison with the annual produce. Gold, and the more durable metals, are things of this sort; ​and also houses. The supply of such things might be at once diminished by destroying them; but to do this could only be the interest of the possessor if he had a monopoly of the article, and could repay himself for the destruction of a part by the increased value of the remainder. The value, therefore, of such things may continue for a long time so low, either from excess of supply or falling off in the demand, as to put a complete stop to further production; the diminution of supply by wearing out being so slow a process, that a long time is requisite, even under a total suspension of production, to restore the original value. During that interval the value will be regulated solely by supply and demand, and will rise very gradually as the existing stock wears out, until there is again a remunerating value, and production resumes its course.
Finally, there are commodities of which, though capable of being increased or diminished to a great, and even an unlimited extent, the value never depends upon anything but demand and supply. This is the case, in particular, with the commodity Labour; of the value of which we have treated copiously in the preceding Book: and there are many cases besides, in which we shall find it necessary to call in this principle to solve difficult questions of exchange value This will be particularly exemplified when we treat of International Values; that is, of the terms of interchange between things produced in different countries, or, to speak more generally, in distant places. But into these questions we cannot enter, until we shall have examined the case of commodities which can be increased in quantity indefinitely and at pleasure; and shall have determined by what law, other than that of Demand and Supply, the permanent or average values of such commodities are regulated. This we shall do in the next chapter.
* ↑ Logic of Political Economy, p. 13.
* ↑ Adam Smith, who introduced the expression "effectual demand," employed it to denote the demand of those who are willing and able to give for the commodity what he calls its natural price, that is, the price which will enable it to be permanently produced and brought to market.—See his chapter on Natural and Market Price (book i. ch. 7.)
* ↑ "The price of corn in this country has risen from 100 to 200 per cent and upwards, when the utmost computed deficiency of the crops has not been more than between one-sixth and one-third below an average, and when that deficiency has been relieved by foreign supplies. If there should be a deficiency of the crops amounting to one-third, without any surplus from a former year, and without any chance of relief by importation, the price might rise five, six, or even tenfold."—Tooke's History of Prices, vol. i. pp. 13-5.
* ↑ See Tooke, and the Report of the Agricultural Committee of 1821.