The Alternative — The Margin, Plate v

Menger had shown that the value of the means of production derives from the value of the ends they serve, leaving a question open: if a resource can serve several ends, what is the cost of devoting it to one? His pupil Friedrich von Wieser answered with an idea so simple, and so far-reaching, that economics has never stopped drawing out its consequences. The cost of using a resource for any purpose, Wieser held, is the value of the best alternative purpose it might have served and now cannot. Cost is not the money paid or the labor spent; cost is the foregone alternative. This is opportunity cost, the marginal idea applied to cost itself, and it teaches that because resources are scarce, every choice forecloses others — so that to choose is always to give something up, and the true price of anything is what one surrenders to obtain it.

The everyday notion of cost is an outlay: what a thing costs is the money one hands over for it, or the labor one pours into it. Wieser saw that this misses what cost truly is. Money and labor matter only because they could have been put to other uses; the real sacrifice in any choice is not the means themselves but the other ends those means might have served. The cost of an hour spent fishing is not the hour but the value of whatever else the hour might have yielded — the wage one might have earned, the rest one might have taken, the work one might have finished. The cost of devoting an acre to wheat is the value of the barley it might have grown instead. Cost, properly understood, is the value of the best alternative forgone, the most valuable opportunity displaced by the choice actually made; and Wieser's name for it, opportunity cost, has become one of the indispensable phrases of the science.¹

1. The everyday notion of cost is outlay — money handed over or labor poured in. Wieser saw this misses cost's nature: money and labor matter only because they could serve other uses, so the real sacrifice is the other ends forgone. The cost of an hour fishing is not the hour but what else it might have yielded; the cost of an acre in wheat, the barley it might have grown. Cost is the value of the best alternative forgone, the opportunity displaced by the choice made — and Wieser's name for it, opportunity cost, is now indispensable.

The idea fits the Austrian theory of value like a keystone. Menger had taught that the value of a means is imputed from the value of the ends it serves; Wieser added that when a means can serve several ends, its cost in any one use is the value it would have had in its best alternative use. The flour that goes into bread has a cost, and that cost is the value of the cakes or the pastry it might have become instead. So cost is not something independent of value, welling up from the side of production to meet demand halfway, as the classical economists had imagined; cost is itself a value — the imputed value of a forgone alternative — and the whole of the classical cost-of-production theory dissolves into the subjective valuations of the marginal school. What had looked like two distinct forces, cost pushing up from below and utility pulling from above, turns out to be one force seen twice: utility, appearing once as the value of the end pursued and again as the value of the end forgone.²

2. The idea is the keystone of Austrian value theory. Menger: a means draws value from the ends it serves; Wieser adds that when a means serves several ends, its cost in one use is its value in the best alternative. Flour's cost in bread is the value of the cakes it might have been. So cost is not independent of value, welling up from production to meet demand; cost is itself a value, the imputed worth of a forgone alternative. The two apparent forces — cost from below, utility from above — are one: utility, seen once as the end pursued, again as the end forgone.

⁂

Opportunity cost is marginalism carried into the reckoning of cost, and it speaks always in the language of the margin. The relevant question is never the total cost of all one's activity but the cost, at the margin, of doing a little more of one thing — and that marginal cost is simply the value of the little less of something else that the scarce resource must now forgo. To spend one more hour at the desk is to spend one fewer hour where it might have done some other good; to commit one more dollar of capital to a venture is to withdraw it from the next best return it could have earned. The cost of one more of anything is the best alternative use of the resources it absorbs, valued at the margin. And because the resources of any person, firm, or society are finite, there is no escaping the reckoning: every margin gained on one front is a margin surrendered on another, and the whole art of economizing is nothing but the continual comparison of what is gained against what must be given up.³

3. Opportunity cost is marginalism carried into cost, speaking always in the margin's language. The question is never total cost but the cost, at the margin, of a little more of one thing — the value of the little less of something else the scarce resource must forgo. One more hour at the desk is one fewer elsewhere; one more dollar in a venture is one withdrawn from its next best return. The cost of one more of anything is the best alternative its resources could have served. Resources being finite, every margin gained is a margin surrendered: economizing is the continual weighing of gain against what is given up.

Few ideas in economics reach as far as opportunity cost, and few are as often forgotten. It is the whole content of the maxim that there is no free lunch: whatever appears to cost nothing has in truth been bought with the alternative it displaced. It underlies the cost of capital, which is not the interest paid but the return the capital might have earned elsewhere — the hurdle every investment must clear. It underlies comparative advantage and the gains from trade, for one should specialize in what one forgoes least by producing. And it carries a sharp correction to common reasoning about cost. A cost already incurred and unrecoverable — what is sunk — is no cost at all to a present decision, because it forecloses no alternative; only the future alternatives a choice gives up are its true costs. Cost, on this understanding, is forward-looking and subjective: not the dead weight of what one has already spent, but the living value of the roads one chooses not to take.⁴

4. Few ideas reach as far, or are as often forgotten. Opportunity cost is the content of there is no free lunch: what seems costless was bought with the alternative it displaced. It underlies the cost of capital (not interest paid but the return forgone elsewhere, the hurdle to clear), comparative advantage, and the gains from trade (specialize where you forgo least). And it corrects common reasoning: a sunk cost, unrecoverable, is no cost to a present choice, for it forecloses no alternative. Cost is forward-looking and subjective — not what one has spent, but the roads one declines to take.

With opportunity cost the marginal account of value is complete on both its sides. On the side of demand, the value of a good is the marginal utility of its last unit; on the side of supply, the cost of a good is the marginal value of the best alternative its making forgoes — and both sides are, at bottom, subjective valuations at the margin. There is no longer a theory of value and a separate theory of cost; there is one marginal principle, governing the worth of what we pursue and the worth of what we surrender to pursue it. It remains only to see this single principle applied not to one good or one choice but to a whole economy at once — to ask how, when every person is equalizing margins across every good, and the cost of each thing is the alternative forgone in its making, all the prices of all the goods come to be settled together. That is the grandest reach of the marginal idea, and the work of the volume's flagship. The next plate is the equilibrium.⁵

5. With opportunity cost the marginal account is complete on both sides: on demand, a good's value is the marginal utility of its last unit; on supply, its cost is the marginal value of the best alternative forgone — both subjective valuations at the margin. No longer a theory of value and a separate theory of cost, but one marginal principle, governing what we pursue and what we surrender to pursue it. It remains to apply it to a whole economy at once — how all prices settle together when everyone equalizes margins. That is the flagship's work. Next: the equilibrium.

Friedrich von Wieser gave the marginal school its theory of cost. The cost of using any scarce resource, he held, is not the money laid out or the labor spent but the value of the best alternative use forgone — opportunity cost, the displaced alternative. The idea completes Menger's imputation, dissolving the classical cost-of-production theory by revealing cost to be itself an imputed value, the worth of the end one gives up; it is the marginal principle applied to cost, for the cost of one more of anything is the best alternative the resources could have served; and it reaches across the whole of economics, from the cost of capital to the gains from trade to the truth that a sunk cost is no cost at all. To choose is always to forgo, and the cost of anything is what one surrenders to obtain it. The next plate is the equilibrium.