Prisoner's dilemma

What is the prisoner’s dilemma?

The prisoner’s dilemma is a game in which each player has an incentive to defect regardless of the other’s choice, yet both would receive better payoffs from mutual cooperation than mutual defection.

Prisoner’s dilemma example

In the familiar fictional story, two suspects choose separately whether to stay silent or betray the other. Suppose mutual silence gives each one year, mutual betrayal gives each five, and a lone betrayer goes free while the silent suspect receives ten. Betrayal reduces each person’s sentence whichever choice the other makes, yet both would do better with mutual silence than mutual betrayal. These are stipulated game payoffs, not a description of real sentencing.

Payoff structure

For example, suppose both players get 3 points if they cooperate and 1 each if both defect. A lone defector gets 5 while the cooperator gets 0. Each player gains by defecting whichever action the other takes, but mutual defection gives both less than mutual cooperation.

The Stanford Encyclopedia of Philosophy entry explains this ordering and distinguishes the one-shot game from repeated and other variants.

Cooperation and repeated interaction

The prediction depends on the specified payoffs and decision setting. Repeated interaction can change strategic incentives. The game does not show that all people inevitably defect or that every conflict is a prisoner’s dilemma. Before applying it to a real setting, identify the available actions, consequences, and what each participant values.