# Coase Theorem Definition

WRITTEN BY **PAUL BOYCE** | Updated 7 January 2021

## What is the Coase Theorem

Coase theorem is the idea that under certain conditions, the issuing of property rights can solve negative externalities. For example, a Forrester will manage their forest to ensure its longevity and protect it from fires. It is their incentive to do so in order for them to be able to sell logs in future years.

The Coase theorem was originally coined by economist, Ronald Coase, in his 1960 paper, ‘The Problem with Social Cost’. He explains that property rights can become conflicting, thereby resulting in inefficient economic results. When property rights are not clearly defined, disputes can arise.

##### Key Points

- Coase theorem is the idea that under certain conditions, the issuing of property rights can solve negative externalities.
- Coase theorem is only applicable when transaction controls are zero.
- There are a number of assumptions to Coase theorem, many of which are not applicable in the real world.

For example, a business may pollute a river. In turn, those that benefit from walking past the river and enjoying the views face a negative externality. There may be bottles and other items in the river which make it unpleasant. Neither the business nor the individual owns the right to the river. What results is a negative cost on to the individual walking past the river. We may then see lawsuits that can drag on for years and cost thousands of dollars.

The Coase theorem states that in such situations, it is more efficient for property rights to be clearly defined and for both parties to bargain instead. Although this is based on the assumption that there are no transaction costs.

So in the previous example, the business may own the right to pollute the river. In turn, the individual would pay the business to use and walk around the river. It would, therefore, benefit the business to reduce its pollution in order to obtain income from the individual.

## Coase Theorem Explained

The Coase Theorem is based on assigned property rights which help to align true economic value. Where property rights are not assigned, we see an inefficient allocation of resources. This may be noise pollution, air pollution, or some other negative externality.

When such negative externalities occur, the Coase theorem states that they can be prevented by assigning property rights and then allowing both parties to bargain. In other words, the Coase theorem suggests that negative externalities can be resolved with property rights. This is best explained with an example.

### Example of the Coase Theorem

There is a farmer who uses fertilizer on his crops to help them grow. However, those fertilizers flow down into the nearby river, which negatively affects those who are fishing downstream. Other members downstream may also become affected.

In this example, the farmer is causing a negative externality onto the fishers. The cost of which is unknown and without property rights, there is no way of accounting for such costs. This is where the Coase theorem kicks in.

Without clearly defined property rights, the farmer and the fisher may become entwined in a long court battle to determine who is in the right. This will cost thousands of dollars, time, and effort. The solution is to assign property rights and allow both parties to negotiate.

If the farmer has defined, divisible, and defendable property rights, he would own the right to use pesticides to help grow his crops. The negative externality will cause a cost onto the fisher. In turn, both parties would have to negotiate what it is worth to reduce or diminish that negative externality.

The fisher would pay the farmer however much it is worth to allow them to fish. That may be $50, $100 or $1,000. The main point is that the price is determined by the value the farmer has to forgo by reducing the amount of fertilizer they use.

So reducing the amount of fertilizer may reduce their crop yield, but they would consequently be compensated by the fishers downstream. In the same fashion, if the fisher owns the river, then the farmer would have to compensate the fisher depending on how much fertilizer gets washed into the river.

The idea behind Coase theorem is that value will be placed on the negative externality. So if the farmer wants to use fertilizer, he must pay the owner of the land, which, in this case, is the fisher. Hence the externality is paid for.

## Coase Theorem Illustrated

To help us understand Coase theorem further, let’s illustrate it below.

As we can see from the chart, we have a negative externality, the fertiliser use on the x-axis. On the y-axis, we have the marginal effect of the externality on both parties. The reason both lines are downwards sloping is that there comes a point where adding extra fertiliser into the river cannot do any more damage than it already has. At the same time, the marginal benefit slope goes to Q2 which refers to the point where there is no additional benefit to the farmer of using more fertiliser.

When there are property rights, the optimal point on the chart would be at Q1 where the marginal benefit is equal to the marginal damage. That way the farmer can produce up to the point by which the fisher is willing to accept and pay to use the river.

When property rights do not exist, the farmer will produce up to point Q2, until there is no further benefit in using more fertilizer. That way, the fisher loses all the welfare between Q1 and Q2. In other words, the damage that is caused between the equilibrium and the actual point that the farmer produces to.

Let us now allocate property rights to the farmer. Under the Coase theorem, this would also mean that there are no transaction costs, property rights are well defined, and are enforceable.

When property rights are allocated, bargaining can occur. In this instance, the fisher can now bargain with the farmer as to how much fertilizer to use. The fisher would prefer the farmer to change production from Q2 (maximum negative externality) to Q1 (socially optimal for both parties). In turn, this will mean that the fisher now gains the amount of welfare shaded in blue.

At the same time, the farmer loses out from shifting his production from Q2 to Q1. Less fertilizer is used, so crop yields can also become affected.

What we can tell from the two charts above, is that the value to the fisher below the marginal damage line and between Q1 and Q2; is greater than the value to the farmer as per the chart above.

In other words, the fisher gains more from the transition than the farmer. In turn, the fisher is willing to pay the farmer more than he loses. Yet less than he is gaining. Therefore, both parties will be better off and we reach the socially optimal level of production.

What we see as a result is a Pareto improvement. This is where both parties are better off and all externalities are internalized. So the market is not working efficiently because of property rights.

## Coase Theorem Assumptions

The Coase theorem only works under certain assumptions. They are:

### 1. No Transaction Costs

When we say there are no transaction costs, this refers to the cost of identifying affect parties or trading partners. For instance, the farmer would have to find fishers downstream in order to bargain with them.

Then, there is the case of the agreement. That may require legal fees that add to the transaction cost. Then, we have compliance. The fisher may want to monitor how much fertilize the farmer is using to ensure he stays within the agreement; another transaction cost.

### 2. Perfect Information

Without perfect information, the socially optimal point will not be reached. We may move closer towards it, but not reach it. This is because, without perfect information, both parties will be unable to determine value. If we look back on the farmer example, if the farmer does not know how much of an impact halving his fertilizer use would have, he is unable to value it effectively.

### 3. Equal Market Power

When we talk about a fisher and a farmer, we may consider them equals. Yet the Coase theorem assumes that both parties have equal power. For instance, Walmart is going to have greater negotiating power with a small farmer that it affects.

In turn, the socially optimal point cannot be reached as the negotiations are skewed in favor of the stronger party; meaning one side is still faced with the negative externality.

## Limitations of Coase Theorem

### 1. Bargaining is difficult

The Coase theorem relies on efficient and effective bargaining between two parties to reach the socially optimal level of production. However, that is easy to show on a graph, but how do two individuals know or even care to reach that level?

At the same time, you may have two parties that are very different. This may be a difference in size and power, which gives them greater negotiating power. Or, the other individual may have more experience in negotiating and is, therefore, able to bargain for a better deal than would otherwise occur.

### 2. Transaction costs are almost never zero

Although one party may own the property right, there are almost always associated transaction costs. For instance, once a bargain is reached, particularly to reduce pollution, it will most likely need policing. That would require some form of inspections or tests to ensure the threshold or agreed quota is not exceeded.

We also have potential legal fees that would be needed to reach a formal and legally binding agreement. There may also be cases where payment is not made which would then require further legal costs in order to collect such dues. For instance, several monthly payments are missed and therefore legal action may be needed.

### 3. Distribution of Income is Affected

Whoever owns the property rights will be the party that ends up receiving the income from the other. So if the farmer owns the rights to the river, the fisher must pay him to use it. At the same time, if the fisher owns the river then it will be the farmer that has to pay.

The issue occurs when we decide who is to own the property. Will it be issued to the highest bidder? If so, income discrepancies may only be extended.

## FAQs on the Coase Theorem

**What is the Coase theorem in economics?**

The Coase theorem is the idea that under certain circumstances, property rights are able to resolve negative externalities.

**Why would the Coase theorem not work?**

The Coase theorem dictates that it only works when transaction costs do not exist. However, in reality, there are always some form of transaction costs. This may be ensuring the agreement is adhered to and monitored, and/or the legal expenses required to draft a legal agreement. Under such circumstances, an equilibrium point is unable to be reached and may cause more costs than the original negative externality imposed.

**How does Coase Theorem seek to solve negative externalities?**

Coase theorem seeks to solve negative externalities by assigning well defined property rights. In turn, two parties can negotiate based on the cost of that externality and the price they are willing to accept in order to reduce such.