Public good

Some things help many people.

A bright lighthouse helps ships. One ship using the light does not stop others. This is a public good.

Street lights and radio are also public goods. These things help us all. Often, the government pays for them. They use tax money to pay for these things. This helps everyone stay safe and learn. It is good to share these things.

A public good is something that helps many people.

It must follow two special rules. First, it is non-excludable. This means you cannot stop people from using it. Second, it is non-rivalrous. This means one person using it does not take it away from others.

Sometimes, people try to use these goods without paying. This is called the "free-rider" problem.

Lighthouses are a great example. One ship seeing the light does not hide it from others. Other examples include street lights, radio, and national security. Knowledge is also a public good. Information about health or the environment can be shared by everyone.

Even national parks can be part of this idea.

Most public goods are provided by the government. The government uses tax money to pay for them. This is because private companies might not make enough money from them. Sometimes, non-profit groups help too. They provide goods that the government might miss. This helps make sure everyone gets what they need.

A public good is a special kind of service or product. It helps many different people at the same time.

To be a true public good, it must follow two rules. First, it is non-excludable. This means you cannot stop people from using it. Second, it is non-rivalrous. This means one person using it does not leave less for someone else.

A lighthouse is a perfect example of this. One ship seeing the light does not make the light dimmer for another ship. Because of these rules, these goods are often provided by the government. They use tax money to pay for things that help everyone.

Public goods can be found in many parts of our lives. They include things like street lighting and broadcast radio. They also include national security and flood control systems.

Even knowledge is a public good. Information about health or the environment can be shared with the whole world. This does not stop anyone else from learning the same facts. Sometimes, these goods are spread across the entire Earth. We call these global public goods. They can include things like videos, pictures, and books that everyone can access.

There are many ways to pay for these important things. Since they are costly, someone must pay the bill. In 1919, an economist named Erik Lindahl had an idea. He suggested a Lindahl tax. This idea says people should pay based on how much they benefit. The more a person gains from a good, the more they pay. This helps the government cover the costs of public utilities. Other ideas, like the VCG mechanism, also help find ways to fund these goods. However, some methods are hard to use in real life because they need too much information.

New ways to fund public goods are always being created. One new idea is called quadratic funding. This was developed by people named Buterin, Hitzig, and Weyl. It uses a special math rule to help decide how much to fund a project. Another idea is called an assurance contract. These were first proposed by Bagnoli and Lipman in 1989. In this system, money is only spent if enough people agree to join. If not enough people sign up, no money is used at all. This makes donors feel safe about their contributions.

Sometimes, public goods face a hard problem called the "free-rider" issue.

This happens when people use a good without paying for it. If too many people do this, the good might not be made at all. To fix this, some goods become "club goods." These have rules to limit access, like toll roads or paid television. Other groups, like non-profits, also help. As Bruce R. Kingma noted, non-profits can provide goods that the government might miss. This ensures that the needs of all citizens are met.

In the study of economics, a public good is a specific type of commodity, product, or service. It is defined by two very important characteristics: non-excludability and non-rivalry. Non-excludability means that it is impossible to prevent people from using the good. Non-rivalry means that one person using the good does not reduce its availability for others. Because of these traits, many people can use a public good at the same time.

Because these goods are often not profitable for private companies to provide, governments typically provide them using tax money.

To understand how these goods work, we must look at the mechanics of rivalry and exclusion. In a non-rivalrous system, your consumption leads to no subtractions from anyone else's consumption. For example, a lighthouse helps ships navigate the sea. One ship seeing the light does not make the light dimmer for the next ship.

In contrast, a common good like wild fish stocks is rivalrous. If too many people harvest the fish, the stock depletes. This limits the access available to others. A public good must be valuable to more than one person to be economically relevant.

Public goods can be categorized into different types based on how they are accessed. Some are considered "pure public goods" when they strictly follow both rules of non-rivalry and non-excludability. Others may become "club goods" if they implement exclusion mechanisms. Common examples of these mechanisms include toll roads, congestion pricing, or pay television with encoded signals. These restrictions allow providers to charge for access.

When people use a good without paying, it creates a "free-rider" problem. This can lead to the good being under-produced, overused, or even degraded.

History shows us how economists have tried to define and fund these goods. Paul A. Samuelson is credited with articulating the modern theory of public goods. In his 1954 paper, "The Pure Theory of Public Expenditure," he used mathematical formalism to describe them. He referred to them as "collective consumption goods." Earlier work by economists like Wicksell and Lindahl helped build the foundation for these ideas.

Understanding these theories helps us decide how to manage shared resources in a modern economy.

There are several complex mechanisms used to fund public goods. In 1919, Erik Lindahl proposed the "Lindahl tax." This theory suggests that individuals should pay for a public good based on the marginal benefit they receive. Essentially, those who benefit more would pay a higher amount. Another method is the Vickrey–Clarke–Groves (VCG) mechanism. This includes the Clarke Pivot Rule to ensure individuals pay into the good. However, VCG is difficult to use in practice because it requires a massive amount of information from every user.

Newer innovations offer different ways to solve funding challenges. Quadratic funding is a modern method developed by Buterin, Hitzig, and Weyl. It uses a subsidy to encourage efficiency, though it can be prone to collusion. Another idea is the "assurance contract," proposed by Bagnoli and Lipman in 1989. In these contracts, money is only spent if the total funding reaches a specific goal. This protects donors from wasting money on projects that lack enough support.

Some even suggest "dominant assurance contracts," which offer a refund bonus if the contract fails.

Public goods also connect to the broader work of non-profit organizations. According to Bruce R. Kingma, non-profits can satisfy demands that the government does not meet. The government usually provides goods based on the needs of the "median voter." This might leave some citizens with less than they desire. Non-profit organizations are financed by donations to fill these gaps. By working alongside governments, these groups ensure that a wider variety of social needs are addressed through collective action.