Rivalry, Excludability & the Four Kinds of Good

You’ll be able to

Classify goods by rivalry and excludability
Explain the free-rider problem and why it prevents private provision
Explain the tragedy of the commons as a rivalry-without-excludability problem

Two properties, four boxes

Rival means one person's consumption reduces what is available to others. Excludable means non-payers can be prevented from consuming. Crossing them gives four categories. Private goods are rival and excludable — a sandwich. Public goods are non-rival and non-excludable — national defense. Common resources are rival but non-excludable — an ocean fishery. Club goods are non-rival but excludable — a streaming service or a toll bridge below capacity.

The classification

rival + excludable = private · non-rival + non-excludable = public · rival + non-excludable = common resource · non-rival + excludable = club good

Public goods are one box of four, not a synonym for "provided by government". Many government-provided goods are private or club goods.

The free-rider problem

If a good is non-excludable, anyone can consume it without paying — so nobody has an incentive to pay. Everyone hopes to free-ride on others' contributions, private provision collapses, and the good is undersupplied or not supplied at all. This is why public goods are typically funded through taxation: compulsion solves the free-rider problem that voluntary payment cannot. Note that non-excludability is what does the work; non-rivalry alone does not create the problem.

The tragedy of the commons

A common resource is rival but non-excludable, which produces overuse rather than undersupply. Each user takes the full private benefit of another fish or another grazing hour while the cost of depletion falls on everyone — a negative externality. So the resource is used past the point where marginal social benefit equals marginal social cost. The remedies all work by supplying the missing excludability: quotas, tradable catch shares, or assigning property rights so an owner has an interest in conservation.

Worked example

Classify each and identify the market failure if any: (a) a lighthouse beam; (b) a public park at capacity on a summer afternoon; (c) an ocean fishery; (d) a subscription news website.

1.(a) Non-rival and non-excludable — a public good. Free-rider problem, so private provision is undersupplied.
2.(b) At capacity it has become rival, and it is non-excludable — a common resource. Congestion is the overuse problem.
3.(c) Rival and non-excludable — a common resource. Tragedy of the commons through overfishing.
4.(d) Non-rival (one more reader costs nothing) but excludable via the paywall — a club good. No market failure of this kind.

Answer: A lighthouse is a public good, a crowded park and a fishery are common resources, and a paywalled site is a club good. Note that the park changed category as it filled: rivalry is a property of the situation, not permanently of the good.

Watch out

"Public good" is a technical classification, not a description of who provides something. Public schooling and public roads are largely rival and excludable — they are government-provided private or club goods. Getting this wrong is the most common error in the unit.

Checkpoint

A good that is rival but non-excludable is:

Checkpoint

The free-rider problem arises specifically from a good being:

Checkpoint

Assigning tradable catch shares to a fishery addresses overfishing by:

On the exam

Answer rivalry and excludability separately and explicitly before naming the category. Rubrics often award the two properties as separate points, and the classification follows automatically once both are stated.

Answer the 3 checkpoints as you read.