Supply and Demand Part 1

Supply and Demand.

by Hubert D. Henderson.

INTRODUCTION

The Theory of Economics does not furnish a body of settled conclusions immediately applicable to policy. It is a method rather than a doctrine, an apparatus of the mind, a technique of thinking, which helps its possessor to draw correct conclusions. It is not difficult in the sense in which mathematical and scientific techniques are difficult; but the fact that its modes of expression are much less precise than these, renders decidedly difficult the task of conveying it correctly to the minds of learners.

Before Adam Smith this apparatus of thought scarcely existed. Between his time and this it has been steadily enlarged and improved. Nor is there any branch of knowledge in the formation of which Englishmen can claim a more predominant part. It is not complete yet, but important improvements in its elements are becoming rare. The main task of the professional economist now consists, either in obtaining a wide knowledge of _relevant_ facts and exercising skill in the application of economic principles to them, or in expounding the elements of his method in a lucid, accurate and illuminating way, so that, through his instruction, the number of those who can think for themselves may be increased.

This Series is directed towards the latter aim. It is intended to convey to the ordinary reader and to the uninitiated student some conception of the general principles of thought which economists now apply to economic problems. The writers are not concerned to make original contributions to knowledge, or even to attempt a complete summary of all the principles of the subject. They have been more anxious to avoid obscure forms of expression than difficult ideas; and their object has been to expound to intelligent readers, previously unfamiliar with the subject, the most significant elements of economic method. Most of the omissions of matter often treated in textbooks are intentional; for as a subject develops, it is important, especially in books meant to be introductory, to discard the marks of the chrysalid stage before thought had wings.

Even on matters of principle there is not yet a complete unanimity of opinion amongst professors. Generally speaking, the writers of these volumes believe themselves to be orthodox members of the Cambridge School of Economics. At any rate, most of their ideas about the subject, and even their prejudices, are traceable to the contact they have enjoyed with the writings and lectures of the two economists who have chiefly influenced Cambridge thought for the past fifty years, Dr. Marshall and Professor Pigou.

J.M. Keynes.

SUPPLY AND DEMAND

CHAPTER I

THE ECONOMIC WORLD

--1. _Theory and Fact_. The controversy between the "Theorist" and the "Practical Man" is common to all branches of human affairs, but it is more than usually prevalent, and perhaps more than usually acrid in the economic sphere. It is always a rather foolish controversy, and I have no intention of entering into it, but its prevalence makes it desirable to emphasize a plat.i.tude. Economic theory must be based upon actual fact: indeed, it must be essentially an attempt, like all theory, to _describe_ the actual facts in proper sequence, and in true perspective; and if it does not do this it is an imposture. Moreover, the facts which economic theory seeks to describe are primarily economic facts, facts, that is to say, which emerge in, and are concerned with, the ordinary business world; and it is, therefore, mainly upon such facts that the theory must be based. People sometimes speak as though they supposed the economist to start from a few psychological a.s.sumptions (e. g. that a man is actuated mainly by his own self-interest) and to build up his theories upon such foundations by a process of pure reasoning. When, therefore, some advance in the study of psychology throws into apparent disrepute such ancient maxims about human nature, these people are disposed to conclude that the old economic theory is exploded, since its psychological premises have been shown to be untrue. Such an att.i.tude involves a complete misunderstanding not merely of economics, but of the processes of human thought. It is quite true that the various branches of knowledge are interrelated very intimately, and that an advance in one will often suggest a development in another. By all means let the economist and psychologist avoid a pedantic specialism and let each stray into the other's province whenever he thinks fit. But the fact remains that they are primarily concerned with different things: and that each is most to be trusted when he is upon his own ground. When, therefore, the economist indulges in a generalization about psychology, even when he gives it as a reason for an economic proposition, in nine cases out of ten the economics will not depend upon the psychology; the psychology will rather be an inference (and very possibly a crude and hasty one) from the economic facts of which he is tolerably sure.

But the purpose of economic theory is not merely to describe the facts of the economic world; it is to describe them in their proper sequence and true perspective. It must begin with those facts which are most general and which have the widest possible significance. Those are not likely to be the facts which our practical experience forces most insistently upon our notice. For it is the particular and not the general, the differences between things rather than their resemblances, that concern us most in daily life. Nor are we likely to find the universal facts which we require in the sphere of public controversy. We must rather look for them in the dark recesses of our consciousness, where are stored those truths which are so obvious that we hardly notice them, which are so indisputable that we seldom examine them, which seem so trite that we are apt to miss their full significance.

--2. _The Division of Labor_. There is one such truth in the economic sphere which it is essential to appreciate vividly and fully, with the widest sweep of the imagination and the sharpest clarity of thought. Man lives by cooperating with his fellow-men. In the modern world, that cooperation is of a boundless range and an indescribable complexity. Yet it is essentially undesigned and uncontrolled by man. The humblest inhabitant of the United States or Great Britain depends for the satisfaction of his simplest needs upon the activities of innumerable people, in every walk of life and in every corner of the globe. The ordinary commodities which appear upon his dinner table represent the final product of the labors of a medley of merchants, farmers, seamen, engineers, workers of almost every craft. But there is no human authority presiding over this great complex of labor, organizing the various units, and directing them towards the common ends which they subserve. Wheel upon wheel, in a ceaseless succession of interdependent processes, the business world revolves: but no one has planned and no one guides the intricate mechanism whose smooth working is so vital to us all. Man, indeed, can organize and has organized much. Within a large factory the efforts of thousands of work-people, each engaged on the repet.i.tion of a single small process, are fitted together so as to form an ordered whole by the conscious direction of the management. Sometimes factory is joined with factory, with farms, fisheries, mines, with transport and distributing agencies, as one gigantic business unit, controlled by a common will. These giant businesses are remarkable achievements of man's organizing gifts. The individuals who control them wield an immense power, which so impresses the public imagination that we dub them "kings," "supermen," "Napoleons of industry." But how small a portion of man's economic life is dominated by such men! Even as regards the affairs of their own businesses, how narrow, after all, are the limits of their influence! The prices at which they can buy their materials and borrow their capital, the quant.i.ties of their products which the public will consume, are factors at once vital to their prosperity and outside their own control.

A great business, like a nation, may cherish visions of self-sufficiency, may stretch its tentacles forward to the consumer and backwards to its supplies of raw material; but each fresh extension of its activities serves only to multiply its points of contact with the outside world. When those points are reached, the largest business, like the smallest, is out on the open sea of an economic system immeasurably larger and more powerful than itself. There it must meet--the better perhaps for its inherent strength and acc.u.mulated knowledge--the impact of rude forces, which it is powerless to control. Beneath the blasts of a trade depression, or some other tendency of world-wide scope, the authority of the mightiest industrial magnate, and equally of any Government, a.s.sumes the same essential insignificance as the pride of a man humbled by contact with the elemental powers of nature.

--3. _The Existence of Order_. The parallel can be pursued further with advantage. Just as in the world of natural phenomena, which for long seemed to man so wayward and inexplicable, we have come gradually to perceive an all-pervading uniformity and order; so there is manifest in the economic world, uniformity, order, of a similar if less majestic kind. Upon the cooperation of his fellowmen, man depends for the very means of life: yet he takes this cooperation for granted, with a complacent confidence and often with a naive unconsciousness, as he takes the rising of to-morrow's sun. The reliability of this unorganized cooperation has powerfully impressed the imagination of many observers.

"On entering Paris which I had come to visit," exclaimed Bastiat some seventy years ago, "I said to myself--Here are a million of human beings who would all die in a short time if provisions of every kind ceased to flow towards this great metropolis. Imagination is baffled when it tries to appreciate the vast multiplicity of commodities which must enter to-morrow through the barriers in order to preserve the inhabitants from falling a prey to the convulsions of famine, rebellion, and pillage. And yet all sleep at this moment, and their peaceful slumbers are not disturbed for a single instant by the prospect of such a frightful catastrophe. On the other hand, eighty departments have been laboring to-day, without concert, without any mutual understanding, for the provisioning of Paris."

The theme may well excite wonder. But wonder should always be watched with a wary eye; for he is apt to bring in his train a hanger-on called wors.h.i.+p, who can do nothing but mischief here. It is a short step from a pa.s.sage like that quoted above to a glorification of the existing system of society, to a defence of all manner of indefensible things; and a cross-grained att.i.tude towards all projects of reform. It is a short step; but it is one which it is quite unjustifiable to take. For the evils of our economic system are too plain to be ignored; too many people have harsh personal experience of the wastefulness of its production, the injustice of its distribution; of its sweating, its unemployment and slums. And when the attempt is made to plaster over evils, such as these with obsequious rhetoric about the majesty of economic law, it is not surprising that the spirit of many men should revolt and that they should retort by denying the existence of order in the business world, by declaring that the spectacle which _they_ see is one of discord, confusion and chaos. And then we are engulfed in a controversy as stale, flat and unprofitable as that between the "theorist" and the "practical man."

The truth is that the language of praise and obloquy is quite inappropriate. In the first place, it may be well to note that the order of which I have spoken manifests itself not merely in those economic phenomena which are beneficial to man, but hardly less in those which work to his hurt. Even in those alternations of good and bad trade, which spell so much unemployment and misery, there is discernible a rhythmic regularity like that of the process of the seasons, or the ebb and flow of the tide. This is not an elegance to be admired. Furthermore, in so far as the order comprises adjustments and tendencies which are beneficial (as, indeed, is mainly true), there is no warrant for a.s.suming that these are either adequate to secure a prosperous community or dependent upon the social arrangements which happen to exist. Let us, therefore, refrain from premature polemics and examine in a spirit of detachment some further aspects of the elaborate, but yet unorganized, cooperation of which so much has been already said.

--4. _Some Reflections upon Joint Products_. A quite inadequate idea of the complexity of this cooperation is obtained by dwelling on the numbers of people who partic.i.p.ate in it, or the immense distances over which it extends. The deficiency can be partially supplied by referring to some of the more obvious of the many subtle interconnections which exist between different commodities and different trades.

There are innumerable groups of commodities (which it is customary to term "joint products") such that the production of one commodity belonging to the group necessarily implies or very greatly facilitates the production of the others. Wool and mutton; beef and hides; cotton and cotton-seed are a few familiar ill.u.s.trations. The important feature of these "joint products" is the fairly precise relation which must exist between the quant.i.ties in which the different products are supplied. If you plant a certain crop of cotton, it will yield you so much cotton lint and so much cotton-seed. You can, of course, if you choose, throw away part of the seed, as indeed at one time planters used to do; but unless you do this, you cannot vary the proportions of the two things which you will have for sale. Similarly, if you keep a flock of sheep, or a herd of cattle, you will obtain wool and mutton in the one case, or beef and hides in the other, in proportions, which indeed you can vary within certain limits by choosing a different breed,[1] but which you cannot radically transform. When, however, we turn to the uses to which these products are put, no similar relation is to be discovered. Cotton lint is used chiefly for making articles of clothing; cotton-seed for crus.h.i.+ng into oil, on the one hand, and cake for cattle fodder on the other. There is no apparent connection of any kind between the demands for these different things, and still less is there any obvious reason why these demands should bear to one another the particular proportions which characterize their respective supplies. It is very much the same with wool and mutton; with beef and hides; with all "joint products." Why should we consume mutton on the one hand and woolen clothing on the other, in a ratio at all commensurate with that in which they are yielded by the sheep?

[Footnote 1: These possibilities of small variation are of very great importance as will be shown in Chapter V, but they do not affect the present argument.]

What, then, might we expect to find if order was nonexistent in the economic world? Surely that some things such as wool would be produced in quant.i.ties many times in excess of the demand for them, quite possibly five, ten, or twenty times in excess; while conversely the supplies of others such as mutton might fall far short of what was required. But in practice we find nothing of the sort. Somehow it comes about that an equilibrium is established between the demand for and the supply of every commodity; and that this applies to wool and mutton, to beef and hides, as surely as to commodities which are produced quite independently. It is true that this equilibrium is a rough, imperfect one; and it may happen that what is called a "glut"

of wool may co-exist for a short period with what is called a scarcity of mutton. But qualifications of this nature are in the strictest sense of the phrase, the exceptions which prove the rule. For the departures from equilibrium which gluts and scarcities represent are always transient and are usually confined within narrow limits. A strong prevailing trend towards an adjustment of demand and supply is unmistakably manifest amid all the vagaries of changing circ.u.mstance.

Let me carry the argument a step further for the benefit of any reader who is restrained by a repugnance too deep and instinctive to be readily overcome, from admitting fairly to his mind that conception of order which I am endeavoring to emphasize. He will in all probability be one who, cheris.h.i.+ng ideals of a better and fairer system of society, looks forward to a time when an organized cooperation will be subst.i.tuted for what he regards as the existing chaos. Let us suppose that his visions were fulfilled as completely as he could desire; and that an immense system of Socialism were in existence, embracing not one country only, but the whole world. Suppose all the difficulties of human perversity and administrative technique to have been surmounted and a wise, disinterested executive to be in supreme control of our business life. Let us suppose all this, and ask only the question: How would this executive treat the humdrum case of wool and mutton? How would it decide the number of sheep it would maintain?

Shall we suppose that it is inspired by the ideal "to each according to his need," and that it resolves accordingly that the commodities which people require for a decent standard of life shall be supplied to them as a matter of course? How, then, would it proceed? It might estimate the amount of woolen clothing which a normal family requires, allowing for differences in climate, and possibly indulging somewhat the caprices of human taste. On this basis, a certain number of sheep would be indicated. It might perform a similar calculation for mutton, and again a certain number of sheep would be indicated. But it would be an extraordinary coincidence if the numbers which resulted from these independent calculations were nearly equal to one another, or were even of the same order of magnitude; and, if they differed widely, what number would our world executive select? Would it decide to waste an immense quant.i.ty of either wool or mutton; or would it decide that it could not, after all, supply the full human needs for one or other of the commodities?

Of course, if the executive were sensible it could solve the problem satisfactorily enough. It could retain the monetary system we know to-day and it could supply the commodities to the consumers, not as a matter of right, but by selling them to them _at a price_. This price it could then move upwards or downwards, raising, say, the price of mutton and reducing that of wool, until it found that the consumption of the two things was adjusted in the required ratio. But if it acted in this manner, what essentially would it be doing? It would be seeking by deliberate contrivance to reproduce, in respect of this particular problem, the very conditions which occur to-day without aim or effort on the part of anyone at all.

The moral of this ill.u.s.tration must not be misinterpreted. It does not show the folly of Socialism or the superiority of Laissez-faire. What it does show is the existence in the economic world of an order more profound and more permanent than any of our social schemes, and equally applicable to them all.

--5. _Some Reflections upon Capital_. Another aspect of the great cooperation is of even greater significance. It embraces not only a mult.i.tude of living men, but it links the present together with the future and the past. The goods and services which we enjoy to-day we owe only in part to the labors of the week, the month, or the year, only in part even to the efforts of our contemporaries. The men, long since dead and forgotten, who built our railways, or sunk our coal mines, or engaged in any of a great variety of tasks, are still contributing to the satisfaction of our daily wants. The expression is not altogether fanciful; for, had it not been reasonable to expect that those labors would be of use to us to-day, many of them in all probability would never have been undertaken. It was to meet our present wants, and even our future wants, that many men toiled on monotonous tasks ten, twenty, thirty years ago. And yet, of course, we should deceive ourselves if we supposed that this was the motive of these men, that our welfare was the centre of their heart's desire. We in our turn dedicate to the future, and often to a distant future, an immense portion of our energies. Let any reader who doubts this, study the statistics of the occupations of the people, and reflect on how long a period must elapse before the labors of this trade or that can fulfil their ultimate function. How long would the period be in the case of a man making bricks, which will later be employed in the erection of a factory, where machinery will be made, to equip an electrical generating station designed to supply, over a period of many years, light, heat, and power to people living in a remote Continent? A longer time, it may be hazarded, than he is accustomed to look ahead.

Like the daily cooperation of living men, this cooperation of past, present and future is essential to the well-being of mankind, and yet it is undesigned and unorganized. As private individuals, men do, indeed, deliberately provide for their own future, and for that of their kith and kin: as the directors of businesses, they try to forecast the trend of demand. But such conscious calculations and deliberate acts would avail little if they stood alone. They are hardly more than the necessary spokes in the great wheel which regulates the relations of past, present and future. The hub of the wheel is an elaborate system of borrowing and lending, essentially similar to the buying and selling of commodities. The private individual in order to provide for his family or for his old age "saves" and "invests." But what exactly does this mean? It means that he transfers so much purchasing power, which he might have spent on his personal pleasures, to some one else in return for the expectation of receiving, year by year in the future, he and his heirs after him, a certain smaller quant.i.ty of purchasing power. The other party to the transaction will be, we may suppose, a business man who enters into it because he sees the opportunity of a promising industrial development, to undertake which he requires more purchasing power than he himself possesses. And, because this transaction is entered into, a smaller number of us will shortly be engaged in making motorcars, or gramaphones, and a larger number of us in making factories and machinery, which will later enhance the world's productive power.

Many transactions of the kind take place daily in modern communities, and their multiplicity gives rise to a ma.s.s of phenomena with which we are all tolerably familiar. We recognize a short-loan market, a stock exchange, a number of "markets" where lenders and borrowers are brought together by the aid of various intermediaries, such as banks, bill brokers, and stock jobbers, who correspond to dealers in commodities. Between these different specialized markets, we are aware of an interconnection so close and strong that we speak more generally of a Capital Market, of which the stock exchange, the short-loan market and so forth, are the component parts. Now, "market"

is a word which was originally used to denote a place where tangible commodities were bought and sold; and the more closely we examine the phenomena of the Capital Market, the more closely do we perceive the profound resemblance between the mechanism of borrowing and lending, and that of buying and selling. Corresponding to the price of a commodity is the rate of interest (in the short-loan market we actually call the rate of Discount "the price of money," and speak of money being cheap or dear); and between the rate of interest, the demand for and the supply of capital there exist relations precisely similar to those between price, demand, and supply in commodity markets. Above all there is the same strong prevailing trend towards an adjustment of demand and supply.

This fundamental resemblance between two such apparently incommensurable things as the buying of material commodities and the borrowing of capital is highly significant; it is another instance of that order in the economic world, of which the reader may now be growing weary. But so difficult is it to see clearly and fully something which one sees, as it were, every day of one's life, that a few more moments of reflection on the special case of capital will be time well spent. Let us revert then to our fantasy of a world socialist commonwealth; and humbly submit another poser to its supreme executive. The question this time will be whether some great constructional work, such, let us say, as the recently mooted Severn barrage scheme, should or should not be undertaken. Let us suppose that the costs and future benefits of the undertaking can be estimated accurately; and that the problem reduces itself to one of expending now a sum, let us say, of $100,000,000, with the prospects of obtaining in the future an income of power, or whatever it may be, worth $5,000,000 per annum. I have a.s.sumed for the sake of simplicity that we shall still be reckoning in terms of money, though possibly the executive may have subst.i.tuted Marxian labor units; but it is quite immaterial to the present argument what the measuring rod may be. The point to be observed is, that it is impossible to tackle the problem at all without the conception of a rate of interest. For suppose that you tried to do without it, and said, "We shall take a long view. The interests of the future are no less our concern than those of the present; we shall not discriminate between them. We shall regard as an enterprise worthy to be undertaken whatever promises to yield in the course of time a return larger than the outlay." Where will this lead you? The particular proposal set out above would clearly pa.s.s the test; for in twenty years the resultant benefits would have added up to a figure equivalent to the initial cost. But equally clearly, the cost might have been more than $100,000,000; it might have been $250,000,000, $500,000,000, whatever figure you care to take, and if you extend the period similarly to fifty or one hundred years, sooner or later the gains would top the cost. Now there is no limit to the enterprises which would pay their way on this basis; and it would be quite impossible to undertake them all. For they would swallow up all and more than all your labor and your materials, and would leave you with no resources with which to meet the recurrent daily wants of men. Clearly, then, in some way or other, you must pick and choose, you must reject some enterprises as _insufficiently_ worth while. But how would you proceed to choose?

Without a clear principle, a simple criterion to guide you, you would be plunged in utter chaos. You could not say, "Let all proposals involving capital expenditure be submitted to a central committee, who shall compare them with one another in a sort of compet.i.tive examination and, after deciding the number of applications they can pa.s.s on the basis of the volume of resources which they can devote to the future, award the places to those which head the list." Such a prospect is a nightmare of officialism and delay. You would be driven to formulate a simple, intelligible rule or measure, and leave that rule to be applied by the unfettered judgment of innumerable men to individual problems, as and when they arose. And for such a rule or measure, you could not do better than a rate of interest; you would have to lay it down that only those projects should be approved which promised a return of 6 per cent, or whatever it might be. Even in deciding what it should be, the limits of your choice would be narrowly confined. If, for instance, you fixed on 1 or 2 per cent, you would probably discover that you had not achieved your object, that the undertakings for distant returns which pa.s.sed this test, still consumed far more resources than you could spare. You would be compelled then to raise the rate until it had cut these enterprises down within manageable limits. But, once more, what essentially would you be doing? You would be using the instrument of the rate of interest to adjust the demand for and supply of capital, though indeed the interest might not be paid away as now to private individuals. You would be reproducing by the method of deliberate trial and error, the adjustments which occur automatically as things are, in the actual world. Once again the most perfectly contrived Utopia would be compelled to pay to the unorganized cooperation of our epoch the sincerest flattery of imitation.

--6. _The Fundamental Character of many Economic Laws_. But again perhaps a word of warning may be desirable. There is much controversy in these days about something called "Capitalism" or "The capitalist system." When these words are used with any precision, they usually refer to the arrangement so prevalent at present, whereby the owners.h.i.+p and sole ultimate control of a business rests with those who hold its stocks and shares. There is much to be said upon the merits and demerits of this system; something will perhaps be said upon the matter in the fifth volume of this series; but I shall not discuss it here. Nothing that I have said so far has any real bearing on it whatsoever; to suppose that it has, is indeed to miss the whole point of this chapter.

The order, which I have sought to reveal, pervading and moving the most diverse phenomena of the economic world, would be a far less noteworthy and impressive thing were it merely the peculiar product of capitalism. Merchant adventurers, companies, and trusts; Guilds, Governments and Soviets may come and go. But under them all, and, if need be, in spite of them all, the profound adjustments of supply and demand will work themselves out and work themselves out again for so long as the lot of man is darkened by the curse of Adam.

CHAPTER II

THE GENERAL LAWS OF SUPPLY AND DEMAND

--1. _Preliminary Statement of Three Laws_. The recognition of order in any branch of natural phenomena is but the prelude to the formulation of a set of laws, the simpler as the order is more universal, which describe, and as we say, explain it. Thus the perception of the even, elliptical courses of the heavenly bodies led to the statement of the law of gravitation and the laws of motion.

In economics, similar laws have long since been enunciated, and have proved themselves such valuable instruments for the understanding of the daily problems of the workaday world, that they have been woven into the texture of our ordinary speech and thought. I have already touched upon them in the preceding chapter. But it is now desirable to set them out in order, in the most concise and formal manner possible.

LAW I. When, at the price ruling, demand exceeds supply, the price tends to rise. Conversely when supply exceeds demand the price tends to fall.

LAW II. A rise in price tends, sooner or later, to decrease demand and to increase supply. Conversely a fall in price tends, sooner or later, to increase demand and to decrease supply.

LAW III. Price tends to the level at which demand is equal to supply.

These three laws are the cornerstone of economic theory. They are the framework into which all a.n.a.lysis of special, detailed problems must be fitted. Their scope is very wide. I have purposely refrained from introducing into my statement of them any reference to commodities; for they extend far beyond commodities. Subject to an important qualification, they apply to capital, the price paid for the use of capital being what we call the rate of interest. They apply hardly less to "services," to the remuneration of labor of every kind and grade. People sometimes protest warmly against the idea of treating labor "like a commodity." If this indignation expresses no more than a belief that in matters concerning conditions of work, and relations between employees and the management, the sensibilities of human nature should be taken into due account, it is based on elementary decency and commonsense. But if, as sometimes appears, it is directed against the fact that the remuneration of labor is controlled by the laws of supply and demand, it is a mere baying at the moon, with singularly little provocation. For these laws are in no way peculiar to commodities, and it is no one's fault that they include commodities too within their scope.

But let us go back to the laws themselves, and probe them and dissect them, and turn them this way and that, so that we may perceive their full content, and grasp it firmly in our minds. The third law implies a prevailing tendency for demand to be equal to supply. This tendency, as was suggested in Chapter I, can be verified by anyone from his experience and observation (provided he is a reasonable person, and not the tiresome kind who would dispute the law of gravitation because he sees that a feather falls to the ground more slowly than a stone). But it can also be deduced as a corollary from the two preceding laws; and to regard it in this way will help us to appreciate its significance. Start, for instance, by supposing that demand is in excess of supply. Then the price will tend to rise. After the price has risen, the supply will become larger, while the demand will fall away. The excess of demand with which we started will thus clearly be diminished. But if there remains any portion of this excess, the same reactions will continue; the price will rise further, and for the same reason; demand will be further checked and supply further stimulated. In other words, these forces must persist until the entire excess of demand over supply is eliminated. If we start by supposing supply to exceed demand, the converse chain of sequences will operate. Now these very simple steps of reasoning illuminate the nature of the normal equilibrium of demand and supply. They reveal that the equilibrium is established and maintained by the agency of _changes in price_, and they enable us to lay it down as perhaps the most important thing that can be said about the price of anything that it will tend to be such as will equate demand and supply. But that is not all that they reveal. They reveal also the extreme dependence of both demand and supply upon price.

Now this is a fact which it is most important to realize vividly. It is apt to be obscured by customary modes of speech. In ordinary times the prices of most commodities and services do not change by very much, unless indeed over a long period of years; the amounts demanded and supplied may therefore seem to maintain a fairly constant level; and we may be tempted to speak of Great Britain producing so many million tons of coal, or America consuming so many millions of motor-cars per annum, almost as though these quant.i.ties were independent of price considerations. But we should never forget that there is no service or commodity produced by man, however essential it may seem, the demand for or the supply of which might not be reduced to nothing, if the price were sufficiently raised on the one hand, or lowered on the other. How easy it is sometimes to forget this simple truth may be seen from the mistake so commonly made of supposing, because the peoples of Central Europe were left, on the cessation of the war, starving and dest.i.tute of the means of life and the materials of work, that they must necessarily become heavy purchasers of imported goods; without pausing to consider whether the prices were such as they could afford to pay.