Principles of Economics by Alfred Marshall (1890)

Book Five: General Relations of Demand, Supply and Value

Chapter 5, Equilibrium of Normal Demand and Supply, Continued, with Reference to Long and Short Periods

1. The variations in the scope of the term Normal, according as the periods of time under discussion are long or short, were indicated in Chapter III. We are now ready to study them more closely.

In this case, as in others, the economist merely brings to light difficulties that are latent in the common discourse of life, so that by being frankly faced they may be thoroughly overcome. For in ordinary life it is customary to use the word Normal in different senses, with reference to different periods of time; and to leave the context to explain the transition from one to another. The economist follows this practice of every-day life: but, by taking pains to indicate the transition, he sometimes seems to have created a complication which in fact he has only revealed.

Thus, when it is said that the price of wool on a certain day was abnormally high though the average price for the year was abnormally low, that the wages of coal-miners were abnormally high in 1872 and abnormally low in 1879, that the (real) wages of labour were abnormally high at the end of the fourteenth century and abnormally low in the middle of the sixteenth; everyone understands that the scope of the term normal is not the same in these various cases.

The best illustrations of this come from manufactures where the plant is long-lived, and the product is short-lived.

When a new textile fabric is first introduced into favour, and there is very little plant suitable for making it, its normal price for some months may be twice as high as those of other fabrics which are not less difficult to make, but for making which there is an abundant stock of suitable plant and skill. Looking at long periods we may say that its normal price is on a par with that of the others: but if during the first few months a good deal of it were offered for sale in a bankrupt's stock we might say that its price was abnormally low even when it was selling for half as much again as the others. Everyone takes the context as indicating the special use of the term in each several case; and a formal interpretation clause is seldom necessary, because in ordinary conversation misunderstandings can be nipped in the bud by question and answer. But let us look at this matter more closely.

We have noticed (1) how a cloth manufacturer would need to calculate the expenses of producing all the different things required for making cloth with reference to the amounts of each of them that would be wanted; and on the supposition in the first instance that the conditions of supply would be normal. But we have yet to take account of the fact that he must give to this term a wider or narrower range, according as he was looking more or less far ahead.

Thus in estimating the wages required to call forth an adequate supply of labour to work a certain class of looms, he might take the current wages of similar work in the neighbourhood: or he might argue that there was a scarcity of that particular class of labour in the neighbourhood, that its current wages there were higher than in other parts of England, and that looking forward over several years so as to allow for immigration, he might take the normal rate of wages at a rather lower rate than that prevailing there at the time. Or lastly, he might think that the wages of weavers all over the country were abnormally low relatively to others of the same grade, in consequence of a too sanguine view having been taken of the prospects of the trade half a generation ago. He might argue that this branch of work was overcrowded, that parents had already begun to choose other trades for their children which offered greater net advantages and yet were not more difficult; that in consequence a few years would see a falling-off in the supply of labour suited for his purpose; so that looking forward a long time he must take normal wages at a rate rather higher than the present average. (2)

Again, in estimating the normal supply price of wool, he would take the average of several past years. He would make allowance for any change that would be likely to affect the supply in the immediate future; and he would reckon for the effect of such droughts as from time to time occur in Australia and elsewhere; since their occurrence is too common to be regarded as abnormal. But he would not allow here for the chance of our being involved in a great war, by which the Australian supplies might be cut off; he would consider that any allowance for this should come under the head of extraordinary trade risks, and not enter into his estimate of the normal supply price of wool.

He would deal in the same way with the risk of civil tumult or any violent and long-continued disturbance of the labour market of an unusual character; but in his estimate of the amount of work that could be got out of the machinery, etc. under normal conditions, he would probably reckon for minor interruptions from trade disputes such as are continually occurring, and are therefore to be regarded as belonging to the regular course of events, that is as not abnormal.

In all these calculations he would not concern himself specially to inquire how far mankind are under the exclusive influence of selfish or self-regarding motives. He might be aware that anger and vanity, jealousy and offended dignity are still almost as common causes of strikes and lockouts, as the desire for pecuniary gain: but that would not enter into his calculations. All that he would want to know about them would be whether they acted with sufficient regularity for him to be able to make a reasonably good allowance for their influence in interrupting work and raising the normal supply price of the goods. (3)

2. The element of time is a chief cause of those difficulties in economic investigations which make it necessary for man with his limited powers to go step by step; breaking up a complex question, studying one bit at a time, and at last combining his partial solutions into a more or less complete solution of the whole riddle. In breaking it up, he segregates those disturbing causes, whose wanderings happen to be inconvenient, for the time in a pound called Caeteris Paribus. The study of some group of tendencies is isolated by the assumption other things being equal: the existence of other tendencies is not denied, but their disturbing effect is neglected for a time. The more the issue is thus narrowed, the more exactly can it be handled: but also the less closely does it correspond to real life. Each exact and firm handling of a narrow issue, however, helps towards treating broader issues, in which that narrow issue is contained, more exactly than would otherwise have been possible. With each step more things can be let out of the pound; exact discussions can be made less abstract, realistic discussions can be made less inexact than was possible at an earlier stage. (4)

Our first step towards studying the influences exerted by the element of time on the relations between cost of production and value may well be to consider the famous fiction of the "Stationary state" in which those influences would be but little felt; and to contrast the results which would be found there with those in the modern world.

This state obtains its name from the fact that in it the general conditions of production and consumption, of distribution and exchange remain motionless; but yet it is full of movement; for it is a mode of life. The average age of the population may be stationary; though each individual is growing up from youth towards his prime, or downwards to old age. And the same amount of things per head of the population will have been produced in the same ways by the same classes of people for many generations together; and therefore this supply of the appliances for production will have had full time to be adjusted to the steady demand.

Of course we might assume that in our stationary state every business remained always of the same size, and with the same trade connection. But we need not go so far as that; it will suffice to suppose that firms rise and fall, but that the "representative" firm remains always of about the same size, as does the representative tree of a virgin forest, and that therefore the economies resulting from its own resources are constant: and since the aggregate volume of production is constant, so also are those economies resulting from subsidiary industries in the neighbourhood, etc. [That is, its internal and external economies are both constant. The price, the expectation of which just induced persons to enter the trade, must be sufficient to cover in the long run the cost of building up a trade connection; and a proportionate share of it must be added in to make up the total cost of production.]

In a stationary state then the plain rule would be that cost of production governs value. Each effect would be attributable mainly to one cause; there would not be much complex action and reaction between cause and effect. Each element of cost would be governed by "natural" laws, subject to some control from fixed custom. There would be no reflex influence of demand; no fundamental difference between the immediate and the later effects of economic causes. There would be no distinction between long-period and short-period normal value, at all events if we supposed that in that monotonous world the harvests themselves were uniform: for the representative firm being always of the same size, and always doing the same class of business to the same extent and in the same way, with no slack times, and no specially busy times, its normal expenses by which the normal supply price is governed would be always the same. The demand lists of prices would always be the same, and so would the supply lists; and normal price would never vary.

But nothing of this is true in the world in which we live. Here every economic force is constantly changing its action, under the influence of other forces which are acting around it. Here changes in the volume of production, in its methods, and in its cost are ever mutually modifying one another; they are always affecting and being affected by the character and the extent of demand. Further all these mutual influences take time to work themselves out, and, as a rule, no two influences move at equal pace. In this world therefore every plain and simple doctrine as to the relations between cost of production, demand and value is necessarily false: and the greater the appearance of lucidity which is given to it by skilful exposition, the more mischievous it is. A man is likely to be a better economist if he trusts to his common sense, and practical instincts, than if he professes to study the theory of value and is resolved to find it easy.

3. The Stationary state has just been taken to be one in which population is stationary. But nearly all its distinctive features may be exhibited in a place where population and wealth are both growing, provided they are growing at about the same rate, and there is no scarcity of land: and provided also the methods of production and the conditions of trade change but little; and above all, where the character of man himself is a constant quantity. For in such a state by far the most important conditions of production and consumption, of exchange and distribution will remain of the same quality, and in the same general relations to one another, though they are all increasing in volume. (5)

This relaxation of the rigid bonds of a purely stationary state brings us one step nearer to the actual conditions of life: and by relaxing them still further we get nearer still. We thus approach by gradual steps towards the difficult problem of the interaction of countless economic causes. In the stationary state all the conditions of production and consumption are reduced to rest: but less violent assumptions are made by what is, not quite accurately, called the statical method. By that method we fix our minds on some central point: we suppose it for the time to be reduced to a stationary state; and we then study in relation to it the forces that affect the things by which it is surrounded, and any tendency there may be to equilibrium of these forces. A number of these partial studies may lead the way towards a solution of problems too difficult to be grasped at one effort. (6)

4. We may roughly classify problems connected with fishing industries as those which are affected by very quick changes, such as uncertainties of the weather; or by changes of moderate length, such as the increased demand for fish caused by the scarcity of meat during the year or two following a cattle plague; or lastly, we may consider the great increase during a whole generation of the demand for fish which might result from the rapid growth of a high-strung artisan population making little use of their muscles.

The day to day oscillations of the price of fish resulting from uncertainties of the weather, etc., are governed by practically the same causes in modern England as in the supposed stationary state. The changes in the general economic conditions around us are quick; but they are not quick enough to affect perceptibly the short-period normal level about which the price fluctuates from day to day: and they may be neglected [impounded in caeteris paribus] during a study of such fluctuations.

Let us then pass on; and suppose a great increase in the general demand for fish, such for instance as might arise from a disease affecting farm stock, by which meat was made a dear and dangerous food for several years together. We now impound fluctuations due to the weather in caeteris paribus, and neglect them provisionally: they are so quick that they speedily obliterate one another, and are therefore not important for problems of this class. And for the opposite reason we neglect variations in the numbers of those who are brought up as seafaring men: for these variations are too slow to produce much effect in the year or two during which the scarcity of meat lasts. Having impounded these two sets for the time, we give our full attention to such influences as the inducements which good fishing wages will offer to sailors to stay in their fishing homes for a year or two, instead of applying for work on a ship. We consider what old fishing boats, and even vessels that were not specially made for fishing, can be adapted and sent to fish for a year or two. The normal price for any given daily supply of fish, which we are now seeking, is the price which will quickly call into the fishing trade capital and labour enough to obtain that supply in a day's fishing of average good fortune; the influence which the price of fish will have upon capital and labour available in the fishing trade being governed by rather narrow causes such as these. This new level about which the price oscillates during these years of exceptionally great demand, will obviously be higher than before. Here we see an illustration of the almost universal law that the term Normal being taken to refer to a short period of time an increase in the amount demanded raises the normal supply price. This law is almost universal even as regards industries which in long periods follow the tendency to increasing return. (7)

But if we turn to consider the normal supply price with reference to a long period of time, we shall find that it is governed by a different set of causes, and with different results. For suppose that the disuse of meat causes a permanent distaste for it, and that an increased demand for fish continues long enough to enable the forces by which its supply is governed to work out their action fully (of course oscillations from day to day and from year to year would continue: but we may leave them on one side). The source of supply in the sea might perhaps show signs of exhaustion, and the fishermen might have to resort to more distant coasts v, and to deeper waters, Nature giving a Diminishing Return to the increased application of capital and labour of a given order of efficiency. On the other hand, those might turn out to be right who think that man is responsible for but a very small part of the destruction of fish that is constantly going on; and in that case a boat starting with equally good appliances and an equally efficient crew would be likely to get nearly as good a haul after the increase in the total volume of the fishing trade as before. In any case the normal cost of equipping a good boat with an efficient crew would certainly not be higher, and probably be a little lower after the trade had settled down to its now increased dimensions than before. For since fishermen require only trained aptitudes, and not any exceptional natural qualities, their number could be increased in less than a generation to almost any extent that was necessary to meet the demand; while the industries connected with building boats, making nets, etc. being now on a larger scale would be organized more thoroughly and economically. If therefore the waters of the sea showed no signs of depletion of fish, an increased supply could be produced at a lower price after a time sufficiently long to enable the normal action of economic causes to work itself out: and, the term Normal being taken to refer to a long period of time, the normal price of fish would decrease with an increase in demand. (8)

Thus we may emphasize the distinction already made between average price and normal price. An average may be taken of the prices of any set of sales extending over a day or a week or a year or any other time: or it may be the average of sales at any time in many markets; or it may be the average of many such averages. But the conditions which are normal to any one set of sales are not likely to be exactly those which are normal to the others: and therefore it is only by accident that an average price will be a normal price; that is, the price which any one set of conditions tends to produce. In a stationary state alone, as we have just seen, the term normal always means the same thing: there, but only there, "average price" and "normal price" are convertible terms. (9)

5. To go over the ground in another way. Market values are governed by the relation of demand to stocks actually in the market; with more or less reference to "future" supplies, and not without some influence of trade combinations.

But the current supply is in itself partly due to the action of producers in the past; and this action has been determined on as the result of a comparison of the prices which they expect to get for their goods with the expenses to which they will be put in producing them. The range of expenses of which they take account depends on whether they are merely considering the extra expenses of certain extra production with their existing plant, or are considering whether to lay down new plant for the purpose. In the case, for instance, of an order for a single locomotive, which was discussed a little while ago (10), the question of readjusting the plant to demand would hardly arise: the main question would be whether more work could conveniently be got out of the existing plant. But in view of an order for a large number of locomotives to be delivered gradually over a series of years, some extension of plant "specially" made for the Purpose, and therefore truly to be regarded as prime marginal costs would almost certainly be carefully considered.

Whether the new production for which there appears to be a market be large or small, the general rule will be that unless the price is expected to be very low that portion of the supply which can be most easily produced, with but small prime costs, will be produced: that portion is not likely to be on the margin of production. As the expectations of price improve, an increased part of the production will yield a considerable surplus above prime costs, and the margin of production will be pushed outwards. Every increase in the price expected will, as a rule, induce some people who would not otherwise have produced anything, to produce a little; and those, who have produced something for the lower price, will produce more for the higher price. That part of their production with regard to which such persons are on the margin of doubt as to whether it is worth while for them to produce it at the price, is to be included together with that of the persons who are in doubt whether to produce at all; the two together constitute the marginal production at that price. The producers, who are in doubt whether to produce anything at all, may be said to lie altogether on the margin of production (or) if they are agriculturists, on the margin of cultivation). But as a rule they are very few in number, and their action is less important than that of those who would in any case produce something.

The general drift of the term normal supply price is always the same whether the period to which it refers is short or long; but there are great differences in detail. In every case reference is made to a certain given rate of aggregate production; that is, to the production of a certain aggregate amount daily or annually. In every case the price is that the expectation of which is sufficient and only just sufficient to make it worth while for people to set themselves to produce that aggregate amount; in every case the cost of production is marginal; that is, it is the cost of production of those goods which are on the margin of not being produced at all, and which would not be produced if the price to be got for them were expected to be lower. But the causes which determine this margin vary with the length of the period under consideration. For short periods people take the stock of appliances for production as practically fixed; and they are governed by their expectations of demand in considering how actively they shall set themselves to work those appliances. In long periods they set themselves to adjust the flow of these appliances to their expectations of demand for the goods which the appliances help to produce. Let us examine this difference closely.

6. The immediate effect of the expectation of a high price is to cause people to bring into active work all their appliances of production, and to work them full time and perhaps overtime. The supply price is then the money cost of production of that part of the produce which forces the undertaker to hire such inefficient labour (perhaps tired by working overtime) at so high a price, and to put himself and others to so much strain and inconvenience that he is on the margin of doubt whether it is worth his while to do it or not. The immediate effect of the expectation of a low price is to throw many appliances for production out of work, and slacken the work of others; and if the producers had no fear of spoiling their markets, it would be worth their while to produce for a time for any price that covered the prime costs of production and rewarded them for their own trouble.

But, as it is, they generally hold out for a higher price; each man fears to spoil his chance of getting a better price later on from his own customers; or, if he produces for a large and open market, he is more or less in fear of incurring the resentment of other producers, should he sell needlessly at a price that spoils the common market for all. The marginal production in this case is the production of those whom a little further fall of price would cause, either from a regard to their own interest or by formal or informal agreement with other producers, to suspend production for fear of further spoiling the market. The price which, for these reasons, producers are just on the point of refusing, is the true marginal supply price for short periods. It is nearly always above, and generally very much above the special or prime cost for raw materials, labour and wear-and-tear of plant, which is immediately and directly involved by getting a little further use out of appliances which are not fully employed. This point needs further study.

In a trade which uses very expensive plant, the prime cost of goods is but a small part of their total cost; and an order at much less than their normal price may leave a large surplus above their prime cost. But if producers accept such orders in their anxiety to prevent their plant from being idle, they glut the market and tend to prevent prices from reviving. In fact however they seldom pursue this policy constantly and without moderation. If they did, they might ruin many of those in the trade, themselves perhaps among the number; and in that case a revival of demand would find little response in supply, and would raise violently the prices of the goods produced by the trade. Extreme variations of this kind are in the long run beneficial neither to producers nor to consumers; and general opinion is not altogether hostile to that code of trade morality which condemns the action of anyone who "spoils the market" by being too ready to accept a price that does little more than cover the prime cost of his goods, and allows but little on account of his general expenses. (11)

For example, if at any time the prime cost, in the narrowest sense of the word, of a bale of cloth is 100; and if another 100 are needed to make the cloth pay its due share of the general expenses of the establishment, including normal profits to its owners, then the practically effective supply price is perhaps not very likely to fall below 150 under ordinary conditions, even for short periods; though of course a few special bargains may be made at lower prices without much affecting the general market.

Thus, although nothing but prime cost enters necessarily and directly into the supply price for short periods, it is yet true that supplementary costs also exert some influence indirectly. A producer does not often isolate the cost of each separate small parcel of his output; he is apt to treat a considerable part of it, even in some cases the whole of it, more or less as a unit. He inquires whether it is worth his while to add a certain new line to his present undertakings, whether it is worth while to introduce a new machine and so on. He treats the extra output that would result from the change more or less as a unit beforehand; and afterwards he quotes the lowest prices, which he is willing to accept, with more or less reference to the whole cost of that extra output regarded as a unit.

In other words he regards an increase in his processes of production, rather than an individual parcel of his products, as a unit in most of his transactions. And the analytical economist must follow suit, if he would keep in close touch with actual conditions. These considerations tend to blur the sharpness of outline of the theory of value: but they do not affect its substance. (12)

To sum up then as regards short periods. The supply of specialized skill and ability, of suitable machinery and other material capital, and of the appropriate industrial organization has not time to be fully adapted to demand; but the producers have to adjust their supply to the demand as best they can with the appliances already at their disposal. On the one hand there is not time materially to increase those appliances if the supply of them is deficient; and on the other, if the supply is excessive, some of them must remain imperfectly employed, since there is not time for the supply to be much reduced by gradual decay, and by conversion to other uses. Variations in the particular income derived from them do not for the time affect perceptibly the supply; and do not directly affect the price of the commodities produced by them. The income is a surplus of total receipts over prime cost; [that is, it has something of the nature of a rent as will be seen more clearly in chapter VIII]. But unless it is sufficient to cover in the long run a fair share of the general costs of the business, production will gradually fall off. In this way a controlling influence over the relatively quick movements of supply price during short periods is exercised by causes in the background which range over a long period; and the fear of "spoiling the market" often makes those causes act more promptly than they otherwise would.

7. In long periods on the other hand all investments of capital and effort in providing the material plant and the organization of a business, and in acquiring trade knowledge and specialized ability, have time to be adjusted to the incomes which are expected to be earned by them: and the estimates of those incomes therefore directly govern supply, and are the true long-period normal supply price of the commodities produced.

A great part of the capital invested in a business is generally spent on building up its internal organization and its external trade connections. If the business does not prosper all that capital is lost, even though its material plant may realize a considerable part of its original cost. And anyone proposing to start a new business in any trade must reckon for the chance of this loss. If himself a man of normal capacity for that class of work, be may look forward ere long to his business being a representative one, in the sense in which we have used this term, with its fair share of the economies of production on a large scale. If the net earnings of such a representative business seem likely to be greater than he could get by similar investments in other trades to which he has access, he will choose this trade. Thus that investment of capital in a trade, on which the price of the commodity produced by it depends in the long run, is governed by estimates on the one hand of the outgoings required to build up and to work a representative firm, and on the other of the incomings, spread over a long period of time, to be got by such a price.

At any particular moment some businesses will be rising and others falling: but when we are taking a broad view of the causes which govern normal supply price, we need not trouble ourselves with these eddies on the surface of the great tide. Any particular increase of production may be due to some new manufacturer who is struggling against difficulties, working with insufficient capital, and enduring great privations in the hope that he may gradually build up a good business. Or it may be due to some wealthy firm which by enlarging its premises is enabled to attain new economies, and thus obtain a larger output at a lower proportionate cost: and, as this additional output will be small relatively to the aggregate volume of production in the trade, it will not much lower the price; so that the firm will reap great gains from its successful adaptation to its surroundings. But while these variations are occurring in the fortunes of individual businesses, there may be a steady tendency of the long-period normal supply price to diminish, as a direct consequence of an increase in the aggregate volume of production.

8. Of course there is no hard and sharp line of division between "long" and "short" periods. Nature has drawn no such lines in the economic conditions of actual life; and in dealing with practical problems they are not wanted. Just as we contrast civilized with uncivilized races, and establish many general propositions about either group, though no hard and fast division can be drawn between the two; so we contrast long and short periods without attempting any rigid demarcation between them. If it is necessary for the purposes of any particular argument to divide one case sharply from the other, it can be done by a special interpretation clause: but the occasions on which this is necessary are neither frequent nor important.

Four classes stand out. In each, price is governed by the relations between demand and supply. As regards market prices, Supply is taken to mean the stock of the commodity in question which is on hand, or at all events " in sight." As regards normal prices, when the term Normal is taken to relate to short periods of a few months or a year, supply means broadly what can be produced for the price in question with the existing stock of plant, personal and impersonal, in the given time. As regards normal prices, when the term Normal is to refer to long periods of several years, Supply means what can be produced by plant, which itself can be remuneratively produced and applied within the given time; while lastly, there are very gradual or Secular movements of normal price, caused by the gradual growth of knowledge, of population and of capital, and the changing conditions of demand and supply from one generation to another. (13)

The remainder of the present volume is chiefly concerned with the third of the above classes: that is, with the normal relations of wages, profits, prices, etc., for rather long periods. But occasionally account has to be taken of changes that extend over very many years; and one chapter, Book VI, ch. XII, is given up to "The Influence of Progress on Value," that is, to the study of secular changes of value.


1. V, III, section 5.

2. There are indeed not many occasions on which the calculations of a business man for practical purposes need to look forward so far, and to extend the range of the term Normal over a whole generation: but in the broader applications of economic science it is sometimes necessary to extend the range even further, and to take account of the slow changes that in the course of centuries affect the supply price of the labour of each industrial grade.

3. Compare I, II, section 7.

4. As has been explained in the Preface, pp. vi-ix, this volume is concerned mainly with normal conditions; and these are sometimes described as Statical. But in the opinion of the present writer the problem of normal value belongs to economic Dynamics: partly because Statics is really but a branch of Dynamics, and partly because all suggestions as to economic rest, of which the hypothesis of a Stationary state is the chief, are merely provisional, used only to illustrate particular steps in the argument, and to be thrown aside when that is done.

5. See below, V, XII, section 3; and compare Keynes, Scope and Method of Political Economy, VI, 2.

6. Compare the Preface and Appendix H, section 4.

7. See V, XII, section I.

8. Tooke (History of Prices, Vol. I, p. 104) tells us: "There are particular articles of which the demand for naval and military purposes forms so large a proportion to the total supply, that no diminution of consumption by individuals can keep pace with the immediate increase of demand by government; and consequently, the breaking out of a war tends to raise the price of such articles to a great relative height. But even of such articles, if the consumption were not on a progressive scale of increase so rapid that the supply, with all the encourage ment of a relatively high price, could not keep pace with the demand, the tendency is (supposing no impediment, natural or artificial, to production or importation) to occasion such an increase of quantity, as to reduce the price to nearly the same level as that from which it had advanced. And accordingly it will be observed, by reference to the table of prices, that salt petre, hemp, iron, etc., after advancing very considerably under the influence of a greatly extended demand for military and naval purposes, tended downwards again whenever that demand was not progressively and rapidly increasing." Thus a continuously progressive increase in demand may raise the supply price of a thing even for several years together; though a steady increase of demand for that thing, at a rate not too great for supply to keep pace with it, would lower price.

9. V, III, section 6. The distinction will be yet further discussed in V, XII and Appendix H. See also Keynes, Scope and Method of Political Economy, ch. VII.

10. pp. 360-7.

11. Where there is a strong combination, tacit or overt, producers may sometimes regulate the price for a considerable time together with very little reference to cost of production. And if the leaders in that combination were those who had the best facilities for production, it might be said, in apparent though not in real contradiction to Ricardo's doctrines, that the price was governed by that part of the supply which was most easily produced. But as a fact, those producers whose finances are weakest, and who are bound to go on producing to escape failure, often impose their policy on the rest of the combination: insomuch that it is a common saying, both in America and England, that the weakest members of a combination are frequently its rulers.

12. This general description may suffice for most purposes: but in chapter XII there will be found a more detailed study of that extremely complex notion, a marginal increment in the processes of production by a representative firm; together with a fuller explanation of the necessity of referring our reasonings to the circumstances of a representative firm, especially when we are considering industries which show a tendency to increasing return.

13. Compare the first section of this chapter. Of course the periods required to adapt the several factors of production to the demand may be very different; the number of skilled compositors, for instance, cannot be increased nearly as fast as the supply of type and printing presses. And this cause alone would prevent any rigid division being made between long and short periods. But in fact a theoretically perfect long period must give time enough to enable not only the factors of production of the commodity to be adjusted to the demand, but also the factors of production of those factors of production to be adjusted and so on; and this, when carried to its logical consequences, will be found to involve the supposition of a stationary state of industry, in which the requirements of a future age can be anticipated an indefinite time beforehand. Some such assumption is indeed unconsciously implied in many popular renderings of Ricardo's theory of value, if not in his own versions of it; and it is to this cause more than any other that we must attribute that simplicity and sharpness of outline, from which the economic doctrines in fashion in the first half of this century derived some of their seductive charm, as well as most of whatever tendency they may have to lead to false practical conclusions.

Relatively short and long period problems go generally on similar lines. In both use is made of that paramount device, the partial or total isolation for special study of some set of relations. In both opportunity is gained for analysing and comparing similar episodes, and making them throw light upon one another; and for ordering and co-ordinating facts which are suggestive in their similarities, and are still more suggestive in the differences that peer out through their similarities. But there is a broad distinction between the two cases. In the relatively short-period problem no great violence is needed for the assumption that the forces not specially under consideration may be taken for the time to be inactive. But violence is required for keeping broad forces in the pound of Caeteris Paribus during, say, a whole generation, on the ground that they have only an indirect bearing on the question in hand. For even indirect influences may produce great effects in the course of a generation, if they happen to act cumulatively; and it is not safe to ignore them even provisionally in a practical problem without special study. Thus the uses of the statical method in problems relating to very long periods are dangerous; care and forethought and self-restraint are needed at every step. The difficulties and risks of the task reach their highest point in connection with industries which conform to the law of Increasing Return; and it is just in connection with those industries that the most alluring applications of the method are to be found. We must postpone these questions to chapter XII and Appendix H.

But an answer may be given here to the objection that since "the economic world is subject to continual changes, and is becoming more complex,... the longer the run the more hopeless the rectification": so that to speak of that position which value tends to reach in the long run is to treat "variables as constants." (Devas, Political Economy, Book IV, ch. v.) It is true that we do treat variables provisionally as constants. But it is also true that this is the only method by which science has ever made any great progress in dealing with complex and changeful matter, whether in the physical or moral world. See above V, v, section 2.

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