Plate iv in print

The Neighbor

Coase's reply: that the harm is reciprocal and has no villain, and that neighbors with clear rights and a way to bargain will reach the same efficient end whoever the law first favors.

The smoke harms the laundry only because the two are neighbors; stop the smoke, and you harm the factory instead. The question is not who wrongs whom, but which use of the air is worth the more.

— the reframing of this plate, after Ronald Coase, 1960

Pigou's tax charges the polluter, and in doing so assumes the polluter is the party at fault. Ronald Coase, in a paper that would remake the field, denied the assumption at its root. The harm of the smoke, he argued, is not something the factory does to the laundry; it is something the two of them do together, by being where they are — and once that is seen, the whole question of the externality changes shape.

The insight Coase pressed is that external harms are reciprocal. We are inclined to say the factory harms the laundry, and to stop there, as though the factory were active and the laundry merely a victim. But the harm exists only because both are present: were there no laundry downwind, the smoke would harm no one; were there no factory, the laundry would stay clean. To protect the laundry by silencing the factory is not to prevent a harm but to shift it — from the laundry, which would have suffered dirty wash, to the factory, which now suffers idleness. Each party's activity is incompatible with the other's; the conflict is symmetric; and there is no natural sense in which one of them, rather than the other, is the cause. The smoke and the wash are rival claimants on a single thing — the use of the air — and the real question is not who is guilty but which claim is worth more.1

1. Coase's reciprocity (Ronald Coase, "The Problem of Social Cost," 1960): external harm is jointly produced by both activities, not caused by one. Restraining the "polluter" merely shifts the harm to him. There is no natural causer; the activities are rival uses of a shared resource, and the question becomes which use is more valuable, not who is at fault.

From this reframing Coase drew a startling conclusion. Suppose the right to the air is clearly assigned — either the factory has the right to smoke, or the neighbors have the right to clean air — and suppose the parties can bargain freely, at no cost. Then, Coase showed, they will reach the efficient outcome whichever way the right was assigned. If clean air is worth more to the neighbors than smoking is to the factory, then either the neighbors, owning the right, refuse to sell it, or the factory, owning the right, is paid by the neighbors to stop — and either way the smoke ceases, because that is the efficient result. If smoking is worth more than clean air, the reverse: either the factory smokes by right, or the neighbors sell it the right to do so, and either way the smoke continues. The assignment of the right determines who pays whom — it is a matter of distribution, of who ends up richer — but not what finally happens, which is efficient regardless. This is the Coase theorem, and its claim is radical: that with clear rights and free bargaining, externalities cure themselves, and no tax is needed at all.2

2. The Coase theorem: with well-defined property rights and zero transaction costs, parties bargain to the efficient allocation regardless of who holds the right; the assignment affects only the distribution of wealth (who pays whom), not the efficient outcome. Externalities, on this view, are resolved by private bargaining without Pigovian taxation — the right going, in effect, to whoever values it most.
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The theorem turns Pigou's framing on its head. Where Pigou saw a harm to be taxed, Coase saw a right to be assigned and a bargain to be struck; where Pigou charged the polluter as a matter of course, Coase showed that charging the polluter and charging the victim lead to the same efficient outcome, differing only in who bears the cost. And it recasts the externality itself. The smoke is an uncounted cost not because the market has failed in some mysterious way, but because there is no market in the one thing at issue — the use of the air — for no one owns it, and so no one can sell it. The externality, on Coase's telling, is the symptom of a missing market; and the cure is not necessarily to tax the harm but, often, to supply the market: to define the right to the air, and let it be bought and sold like anything else, so that the smoke acquires a price through trade.3

3. Coase recasts the externality as a missing market: the cost is uncounted because no one owns the resource (the air) and so it cannot be traded. The implied cure is to define and assign the property right and let bargaining price the externality — shifting the policy question from "what tax?" to "what rights, and can they be traded?" The permit schemes of The Permit operationalize this.

But Coase was not the libertarian his theorem is sometimes taken to make him, and the limit he himself stressed is decisive. The theorem holds only when bargaining is costless — and bargaining is almost never costless. When the smoke falls not on one laundry but on a million households, scattered and unorganized, the cost of gathering them to negotiate, of agreeing among themselves, of preventing each from holding out for a larger share or free-riding on the others' efforts, is so vast that no bargain is struck at all. The transaction costs swamp the gains, and the parties, unable to deal, are left with whatever the law's initial assignment gave them — efficient or not. Coase's real lesson, then, is not that externalities always cure themselves, but that they cure themselves when transaction costs are low and fester when transaction costs are high — and that since the great externalities, the ones that matter most, involve multitudes who cannot possibly bargain, the choice of how to assign the right in the first place, and whether to tax or regulate where no bargain is possible, is exactly what matters.4

4. Coase stressed that the theorem requires low transaction costs; with many scattered parties (the usual case for major externalities), the costs of organizing, negotiating, preventing holdouts, and overcoming free-riding bar any bargain. The real Coasean lesson: externalities resolve privately when transaction costs are low and persist when high — so the assignment of rights and the choice of intervention matter most precisely where bargaining fails. See The Holdout.

So Pigou and Coase are not, in the end, simple opposites, but two answers fitted to two conditions. Where the parties are few and can bargain — the factory and its handful of neighbors — Coase's insight holds, and the law need only assign a clear right and let them trade; the tax is unnecessary and may even do harm. Where the parties are many and cannot bargain — the carbon emitters and the world's future, the drivers and the city — Coase's own analysis says the bargain will fail, and some collective hand, whether Pigou's tax or a direct rule or a constructed market in permits, must do what private trade cannot. The deep question that remains, and that the flagship takes up, is what the externality is once we see it through Coase's eyes: not a wrong with a villain, but a cost that falls outside the price because a right has not been drawn — and the matter of where, and by whom, that right should be drawn.5

5. Pigou and Coase suit different conditions: with few parties and low transaction costs, assign rights and let bargaining work (Coase); with many parties and high transaction costs, collective intervention — a tax, a rule, or a constructed permit market — is required, the failure of bargaining vindicating Pigou's instrument if not his framing. The flagship, The Boundary, synthesizes this around the property-rights line.

The neighbor is Coase's great correction: the reminder that the smoke has no villain, that the harm is the joint work of two activities and the question between them is which use of the world is worth the more, and that — where the parties can bargain — a clear right, not a tax, is all the law need supply, for they will trade their way to efficiency whichever way the right was cast. It dissolves the moral picture of the externality into a question of value and of rights, and it relocates the failure from the market's mysterious breakdown to the plain absence of a market in the thing at issue. But a market requires a thing to trade, and a thing to trade requires a right to own. The next plate takes up the boldest application of Coase's insight — the deliberate manufacture of a market where none existed, by the creation of property in the right to pollute.