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In law and economics, the Coase theorem, attributed to Ronald Coase, describes the economic efficiency of an economic allocation or outcome in the presence of externalities. The theorem states that when trade in an externality is possible and there are no transaction costs, bargaining will lead to an efficient outcome regardless of the initial allocation of property rights. In practice, obstacles to bargaining or poorly defined property rights can prevent Coasian bargaining.

This theorem, along with his 1937 paper on the nature of the firm (which also emphasizes the role of transaction costs), earned Coase the 1991 Nobel Prize in Economics. The Coase theorem is an important basis for most modern economic analyses of government regulation, especially in the case of externalities. George Stigler summarized the resolution of the externality problem in the absence of transaction costs in a 1966 economics textbook in terms of private and social cost, and for the first time called it a "theorem." Since the 1960s, a voluminous literature on the Coase theorem and its various interpretations, proofs, and criticism has developed and continues to grow.


The theory

Coase developed his theory when considering the regulation of radio frequencies. Competing radio stations could use the same frequencies and would therefore interfere with each others' broadcasts. The problem faced by regulators was how to eliminate interference and allocate frequencies to radio stations efficiently. What Coase proposed in 1959 was that as long as property rights in these frequencies were well defined, it ultimately did not matter if adjacent radio stations interfered with each other by broadcasting in the same frequency band. Furthermore, it did not matter to whom the property rights were granted. His reasoning was that the station able to reap the higher economic gain from broadcasting would have an incentive to pay the other station not to interfere. In the absence of transaction costs, both stations would strike a mutually advantageous deal. It would not matter whether one or the other station had the initial right to broadcast; eventually, the right to broadcast would end up with the party that was able to put it to the most highly valued use. Of course, the parties themselves would care who was granted the rights initially because this allocation would impact their wealth, but the end result of who broadcasts would not change because the parties would trade to the outcome that was overall most efficient. This counterintuitive insight – that the initial imposition of legal entitlement is irrelevant because the parties will eventually reach the same result – is Coase’s invariance thesis.

Coase's main point, clarified in his article 'The Problem of Social Cost', published in 1960 and cited when he was awarded the Nobel Prize in 1991, was that transaction costs, however, could not be neglected, and therefore, the initial allocation of property rights often mattered. As a result, one normative conclusion sometimes drawn from the Coase theorem is that property rights should initially be assigned to the actors gaining the most utility from them. The problem in real life is that nobody knows ex ante the most valued use of a resource and also, that there exist costs involving the reallocation of resources by government. Another, more refined normative conclusion also often discussed in law and economics is that government should create institutions which minimize transaction costs, so as to allow misallocations of resources to be corrected as cheaply as possible.

Efficiency and Invariance

Because Ronald Coase himself did not originally intend to set forth any one particular theorem, it has largely been the effort of others who have developed the loose formulation of the Coase theorem. What Coase initially provided was fuel in the form of “counterintuitive insight” [1] that externalities necessarily involved more than a single party engaged in conflicting activities and must be treated as a reciprocal problem. His work explored the relationship between the parties and their conflicting activities and the role of assigned rights/liabilities. While the exact definition of the Coase theorem remains unsettled, there are two issues or claims within the theorem: the results will be efficient and the results in terms of resource allocation will be the same regardless of initial assignments of rights/liabilities.


Efficiency version: aside from transaction costs, the prevailing outcome will be efficient

The zero transaction cost condition is taken to mean that there are no impediments to bargaining. Since any inefficient allocation leaves unexploited contractual opportunities, the allocation cannot be a contractual equilibrium. This is a tautology, but an illuminating one. It reveals that corrective taxation is not the only way to internalize negative externalities.

Invariance version: aside from transaction costs, the same efficient outcome will prevail

This version fits the legal cases cited by Coase. If it is more efficient to prevent cattle trampling a farmer's fields by fencing in the farm, rather than fencing in the cattle, the outcome of bargaining will be the fence, regardless of whether victim rights or unrestricted grazing-rights prevail. Subsequent authors have shown that this version of the theorem is not generally true, however. Changing liability placement changes wealth distribution, which in turn affects demand and prices.[2] Most economists believe that wealth effects are small, however.

Equivalence Version

In his UCLA dissertation and in subsequent work, Steven N. S. Cheung (1969) coined an equivalence version of the Coase theorem: aside from transaction costs, all institutional forms are capable of achieving the same efficient allocation. Contracts, extended markets, and corrective taxation are equally capable of internalizing an externality. To be logically correct, some restrictive assumptions are needed. First, spillover effects must be bilateral. This applies to the cases that Coase investigated. Cattle trample a farmer's fields; a building blocks sunlight to a neighbor's swimming pool; a confectioner disturbs a dentist's patients etc. In each case the source of the externality is matched with a particular victim. It does not apply to pollution generally, since there are typically multiple victims. Equivalence also requires that each institution has equivalent property rights. Victim rights in contract law corresponds to victim entitlements in extended markets and to the polluter pays principle in taxation.[3]

Notwithstanding these restrictive assumptions, the equivalence version helps to underscore the Pigouvian fallacies that motivated Coase. Pigouvian taxation is revealed as not the only way to internalize an externality. Market and contractual institutions should also be considered, as well as corrective subsidies. The equivalence theorem also is a springboard for Coase's primary achievement—providing the pillars for the New Institutional Economics. First, the Coasean maximum-value solution becomes a benchmark by which institutions can be compared. And the institutional equivalence result establishes the motive for comparative institutional analysis and suggests the means by which institutions can be compared (according to their respective abilities to economize on transaction costs). The equivalency result also underlies Coase's (1937) proposition that the boundaries of the firm are chosen to minimize transaction costs. Aside from the "marketing costs" of using outside suppliers and the agency costs of central direction inside the firm, whether to put Fisher Body inside or outside of General Motors would have been a matter of indifference.

Application in United States contract and tort law

The Coase Theorem has been used by jurists and legal scholars in the analysis and resolution of disputes involving both contract law and tort law.

In contract law, Coase is often used as a method to evaluate the relative power of the parties during the negotiation and acceptance of a traditional or classical bargained-for contract.

In modern tort law, application of economic analysis to assign liability for damages was popularized by Judge Learned Hand of Second Circuit Court of Appeals in his decision, United States v. Carroll Towing Co. 159 F.2d 169 (2d. Cir. 1947). Judge Hand's holding resolved simply that liability could be determined by applying the formula of B < PL, where B = the burden (economic or otherwise) of adequate protection against foreseeable damages, P = the probability of damage (or loss) occurring and L = the gravity of the resulting injury (loss). This decision flung open the doors of economic analysis in tort cases, thanks in no small part to Judge Hand's popularity among legal scholars.

In resultant scholarship using economic models of analysis, prominently including the Coase theorem, theoretical models demonstrated that, when transaction costs are minimized or nonexistent, the legal appropriation of liability diminishes in importance or disappears completely. In other words, parties will arrive at an economically efficient solution that may ignore the legal framework in place.

For example, two property owners own land on a mountain-side. Property Owner #1's land is upstream from Owner #2 and there is significant, damaging run-off from Owner #1's land to Owner #2's land. Four scenarios are considered:

  1. If a cause of action exists (i.e. #2 could sue #1 for damages and win) and the property damage equals $100 while the cost of building a wall to stop the run-off equals $50, the wall will probably exist. Owner #1 will build the wall, or pay Owner #2 between $1 and $50 to tolerate the run-off.
  2. If a cause of action exists and the damage equals $50 while the cost of a wall is $100, the wall will not exist. Owner #2 may sue, win the case and the court will order Owner #1 to pay #2 $50. This is cheaper than actually building the wall. Courts rarely order persons to do or not do actions: they prefer monetary awards.
  3. If a cause of action does not exist, and the damage equals $100 while the cost of the wall equals $50, the wall will exist. Even though #2 cannot win the lawsuit, he or she will still pay #1 some amount between $51 and $99 to build the wall.
  4. If a cause of action does not exist, and the damage equals $50 while the wall will cost $100, the wall will not exist. #2 cannot win the lawsuit and the economic realities of trying to get the wall built are prohibitive.

The Coase theorem considers all four of these outcomes logical because the economic incentives will be stronger than legal incentives. Pure or traditional legal analysis will expect that the wall will exist in both scenarios where #2 has a cause of action and that the wall will never exist if #2 has no cause of action.

Complications and Criticism

The main criticism often targeted at the Coase theorem is to say that transaction costs are almost always too high for efficient bargaining to happen. For instance, economist James Meade argued that even in a simple case of a beekeeper's bees dusting a nearby farmer's crops, a Coasean bargaining is inefficient. However, it was pointed out that bee-keepers and farmers do indeed make contracts and have for some time [4].

David Friedman has argued that the fact that an "economist as distinguished as Meade assumed an externality problem was insoluble save for government intervention suggests...the range of problems to which the Coasian solution is relevant may be greater than many would at first guess." [5] Friedman is scathing of most critical attacks on the coase theorem.

Meade could be seen as an example of what Coase himself called "blackboard economists"- the finding of inefficiencies in rational choice models and the immediate presumption that public action is required- without ever examining the real world data to examine if the private market has actually failed to correct the inneficiency.[6] Cheung also shows how Meade demonstrates this practise yet again.[7]

Ronald Coase himself asserts that it would be unrealistic to assume there were no costs in the conduction of market transactions, and that these costs are "often extremely costly, sufficiently costly at any rate to prevent many transactions that would be carried out in a world in which the pricing system worked without cost." (Coase, 1960 - first paragraph of section VI.) On the other hand this isn't really a criticism of the theorem itself, since the theorem considers only those situations in which there are no transaction costs. Instead, it is a criticism of applications of the theorem that neglect this crucial assumption- as well as criticisms on the other side, that is those that overemphasize the effects of transaction costs in the running of private Coasian bargainings.

In many cases of externalities, the bargaining may not happen between two economic factors, but instead the parties might be a single large factory versus a thousand landowners nearby. In such situations, say the critics, not only do transaction costs rise extraordinarily high, but bargaining is hindered by basic prisoner's dilemma problems- classic public good problems. However, it must be noted that the fact that these problems exist does not preclude the free market from finding a Coasian solution, nor does it imply that the public market will be more efficient- the public market being beset by the same ineffeciencies wrought by public goods.

A third critique can be found in the work of the critical legal scholar Duncan Kennedy, who argues that the initial allocation always matters in reality.


  1. ^ Andrew Halpin, Disproving the Coase Theorem, 23 Econ. & Phil. 321, 325—27 (2007).
  2. ^ Varian, H 1987 Intermediate Microeconomics
  3. ^ Johansson, P. and J. Roumasset, Apples, Bees and Contracts: A Coase-Cheung Theorem for Positive Spillover Effects. World Economic Forum, Shanghai: Dec, 2002
  4. ^ Johnson, David B. (1973), "Meade, Bees and Externalities", The Journal of Law and Economics 16 (1): 35–52  
  5. ^ Friedman, David D. (2000), Law's Order, Princeton Paperbacks, pp. 41-42  
  6. ^ Coase, R. H. (1988), The Firm The Market and The LAW, pp. 28  
  7. ^ Cheung, Steven N. S., "The Fable of the Bees", The Journal of Law and Economics 16 (1): 11–33  


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