utility declines. The marginal utility of the two exchangeable units must come to equilibrium in the individual's judgment. At this point demand ceases, not because an additional unit of the one good could afford no gratification, but because it would afford less gratification than the other good in which demand must be expressed to be effectual.
The Demand curve
4. Demand thus varies at different ratios of exchange between goods, and may be expressed graphically by a demand curve. This would show for any one man the decline of the marginal utility of each added portion of a good, and these individual demand curves may be united into a demand curve for a group of men. The demand curve expresses graphically what a man would be willing to pay at each particular stage in the increase of goods. We have here come to the very threshold of the subject of markets and exchange.
Elasticity of demand
5. Elasticity of demand, in the case of any good, expresses the degree in which a change in its ratio to other goods will increase the demand. Elasticity varies for different classes of men according to their wealth and to the cost of the goods. If strawberries are a dollar a box in the city market, a slight fall in the price, say to seventy-five cents, will increase the demand but slightly. But if the price is fifteen cents and falls to ten, the increase in the demand will be marked, for the number of consumers to whom a difference of five cents is important is then very great. The demand for the staples is comparatively inelastic. A certain amount of simple food is necessary to support life; an increase in its price will not quickly check the demand. On the other hand, if the price of staple foods falls, no very great increase will take place in the demand.
CHAPTER 5
EXCHANGE IN A MARKET
§ I. EXCHANGE OF GOODS RESULTING FROM DEMAND
Reciprocal demand becomes exchange
1. Exchange in the usual economic sense is the transfer of two goods by two owners, each of whom deems the good taken more than a value-equivalent for the one given. The comparison of goods that has been discussed above is a kind of exchange. When a person chooses one thing rather than another, one form of gratification may be said to be mentally exchanged for another. This is exchange in that person's mind, or subjective exchange. But the word "exchange" as usually employed means an exchange of goods between persons. It is objective exchange, and when the word is used without modification, it is to be understood in the objective sense. In the last chapter were analyzed the motives of the individual man. Robinson Crusoe on his desert island would in very many ways be acted upon by the same motives in reference to economic goods that men are in society. Yet, it is exchange in society and the complicated problems arising from this transfer of goods from person to person that constitute nearly the whole of the subject-matter of political economy.
Exchange is seen to arise out of the differences in the situations of men with reference to goods. The different subjective valuations give rise to demand, and demand leads to exchange. In early societies differences in natural products were the most usual causes of exchange. Salt, though so essential to life, is found in few places. The metals early became indispensable for weapons of defense or for the chase, and were sought far and wide. Rare shells, feathers, jewels, and the precious metals appealed in early times to a universal desire for ornament. Products like these are the objects of a rude sort of exchange in the first simple efforts made to adjust possessions to wants. Within the tribe, differences in the skill and ability of men to produce arrow heads or weapons or ornaments, bring about the exchange of goods.
Mutual advantage in exchange
2. The advantage of exchange consists in the raising of the want-gratifying power of goods to both parties. It generally was assumed by medieval thinkers that if one party to an exchange gained, the other must lose. The mistaken idea prevailed that value is something fixed in the good, and unchangeable. Where the exchange is voluntary (and only that kind is here being considered), it is mutual advantages which make the exchange rational. Many false conclusions on practical questions still result from a failure to grasp this simple truth. It follows from this that the act of exchange is itself useful, for goods having a small importance to men are given a higher importance by being brought into better relations with wants. Merchants, peddlers, traders, and common carriers of all sorts, therefore, are adding to the utility of goods. This idea has been only slowly apprehended, but is now one of the least disputed propositions in economics.
Demand is supply in another aspect
3. Barter is the exchange of goods without the use of money. Either one of the goods traded in cases of barter may be considered as sold, and either one as bought, according as the matter is looked at from the standpoint of the one or the other party to the exchange. Demand, therefore, is supply, and supply is demand when the point of view is shifted from one party to another. The fisherman's demand for venison is expressed in terms of fish; the hunter's demand for fish is expressed in terms of venison. But to the fisherman the venison is the supply offered to him. The term "marginal utility" of a good, therefore, does not refer merely to the demand of the consumer; for it expresses by a single phrase the idea both of demand and of supply. The utility of the goods composing the supply is expressed in terms of the goods that represent demand and vice versa. The only way in which man can give definite, concrete, numerical expression to his desire for goods is to state it in terms of other goods. In expressing numerically, in terms of other objects, an estimate of the utility of an apple, a horse or a house, one inevitably gives expression to a ratio of exchange; demand for one good is the offer of another good.
§ II. BARTER UNDER SIMPLE CONDITIONS
In isolated exchange the price is not economically fixed
1. In isolated exchange, where only two traders engage in barter, their estimates give respectively the upper and the lower figures of the ratio at which the trade can take place. Let us recall the fact that a difference in the relative estimates that men place on goods is the first essential of exchange. Those estimates may be expressed in a ratio; we may say that A will give four apples for one orange, would be glad to give fewer, but will not give more; while B will give one orange for three apples, would be glad to get more apples, but will not take fewer. The outside limits of the ratio at which the exchange must take place will, therefore, be one orange for three or four apples.
A, seller of apples, offers 4 (or fewer) apples for 1 orange.
B, buyer of apples, demands 3 (or more) apples for 1 orange.
There is, in entirely isolated exchange, therefore, a lack of definiteness in the price, much depending on what Adam Smith called the "higgling of the market." In the old-time American horse trade much depended on "bluff"; in such cases it was as important to be able to judge character as to judge horses. A thorough analysis of the trade, however, would probably show that the bargain is concluded at a point which exactly balances the hopes of gain and fears of loss of one of the parties.
Competitive bidding narrows the limits of price
2. Where one-sided competition exists, the ratio of the exchange will be somewhere between the estimates of the two buyers most eager for the last portion offered. By competition
