Public goods and common resources

Think of it like a giant potluck dinner. Some dishes, once they're out, everyone can eat without stopping anyone else, and one person eating doesn't mean less for another. Other dishes are like a big bowl of shared candy – everyone can grab some, but if too many people grab too much, it's all gone!

In economics, we categorize goods (things we want) based on two main ideas:

• Excludability: Can you stop someone from using it if they don't pay? Imagine a movie ticket. If you don't pay, you don't get in. That's excludable. But what about a beautiful sunset? You can't stop anyone from seeing it, so it's non-excludable.
• Rivalry in Consumption: Does one person using it mean there's less for someone else? If you eat a slice of pizza, that slice is gone for everyone else. That's rival. But if you're watching a TV show, your watching it doesn't stop anyone else from watching it at the same time. That's non-rival.

These two ideas help us sort everything into four types of goods: private goods, public goods, common resources, and club goods. We'll focus on the trickier ones: public goods and common resources.

Let's use a lighthouse as a classic example of a public good. Imagine a lighthouse shining its light to guide ships away from dangerous rocks.

1. Non-excludable: Can the lighthouse keeper stop a specific ship from seeing the light if that ship didn't pay? No! Once the light is on, any ship in the area can see it, whether they contributed money or not.
2. Non-rival: Does one ship seeing the light mean another ship can't see it? No! The light guides many ships at the same time without diminishing (making less of) the benefit for any single ship.

Because it's non-excludable, ships might try to be "free riders" (enjoying the benefit without paying). And because it's non-rival, there's no way to charge per use. This is why private companies usually don't build lighthouses; there's no easy way to make money. So, governments often step in to provide them because they benefit everyone.

Let's break down how the problems with public goods and common resources arise:

1. Identify the good: First, figure out if the good is excludable/non-excludable and rival/non-rival.
2. Public Good Problem (Free Rider): If a good is non-excludable (you can't stop people from using it) and non-rival (one person using it doesn't reduce it for others), it's a public good.
3. The Free Rider Incentive: Everyone wants to enjoy the public good (like a fireworks show) but hopes someone else will pay for it.
4. Under-provision: Because everyone tries to free ride, not enough people pay, and the good might not be provided at all, or not enough of it.
5. Common Resource Problem (Tragedy of the Commons): If a good is non-excludable but rival (like fish in the ocean), it's a common resource.
6. The Overuse Incentive: Everyone has access, and each person benefits individually from using more of the resource.
7. Depletion/Degradation: Because individuals don't consider the impact on others, the resource gets used up too quickly or becomes damaged.

Since private markets often struggle with public goods and common resources, the government usually steps in. Think of the government as the grown-up who organizes the potluck and makes sure everyone contributes fairly or sets rules for sharing.

• For Public Goods: The government can provide the good directly (like national defense or public parks) and pay for it using taxes collected from everyone. This forces everyone to contribute, solving the free-rider problem.
• For Common Resources: The government can regulate access (set limits on how much fish can be caught), impose taxes or fees (like a fishing license), or even turn the resource into a private good (assign property rights to parts of the ocean, though this is tricky!). The goal is to make people consider the cost of their actions on others.

Here are some traps students fall into and how to dodge them:

• ❌ Confusing public goods with government-provided goods: Just because the government provides something (like mail service) doesn't automatically make it a public good. Mail service is excludable (you pay for a stamp) and rival (your letter takes up space). ✅ Remember the definitions: A public good MUST be both non-excludable AND non-rival. Use those two tests!
• ❌ Thinking 'free' means public good: A free concert in the park is a public good, but a free sample at a store is not. The sample is excludable (they can choose not to give it to you) and rival (if you eat it, no one else can eat that specific sample). ✅ Focus on the characteristics: Is it excludable? Is it rival? Not whether it costs money at the moment.
• ❌ Mixing up common resources and public goods: Both are non-excludable, but common resources are rival, while public goods are non-rival. ✅ Ask the 'less for others' question: If one person using it means less for someone else, it's rival (common resource). If not, it's non-rival (public good).