What is the Prisoner's Dilemma?

Mary McMahon
Mary McMahon

The prisoner's dilemma is a concept in game theory which is used to illustrate a variety of situations. The concept is also sometimes utilized in fields like psychology and philosophy, when people want to examine why people act in the ways that they do. Credit for the development of the prisoner's dilemma is generally given to a pair of RAND researchers, Merrill Flood and Melvin Dresher, who worked in the 1950s. Albert W. Tucker refined the idea, and christened the concept the “prisoner's dilemma.”

In the prisoner's dilemma, the prisoner who remains silent is sentenced to a longer jail term, while the talkative prisoner walks free.
In the prisoner's dilemma, the prisoner who remains silent is sentenced to a longer jail term, while the talkative prisoner walks free.

Classically, the prisoner's dilemma is presented as a situation involving two prisoners, A and B, who are taken into custody for a crime. The police are aware that evidence is insufficient, so the prisoners are separated and approached individually. Each prisoner is told that if he or she speaks and turns the other prisoner in while that prisoner remains silent, the talkative prisoner will go free, while the silent prisoner will do jail time. If both prisoners speak up, they will both do some jail time, although the sentence would be shorter than that for a prisoner who remained silent while another spoke, and if both prisoners remain silent, they will each be given a very short prison sentence.

Because of the way in which the prisoner's dilemma is set up, people quickly come to the conclusion that defecting and turning the other prisoner in is the best way to respond to the situation. By remaining silent, a prisoner runs the risk of being hit with a long sentence while the other prisoner walks. By speaking, a prisoner can hope that the other prisoner stays silent, in which case he or she goes free. Of course, when both prisoners speak, they both get some jail time, but the risk of remaining silent is perceived as far greater than the risk of speaking.

As a thought experiment, the prisoner's dilemma is very interesting, and some psychology classes play a real-world version to show students how it works. It plays on the idea that people caught in challenging situations usually try to guess what other people will do. In the case of the prisoner's dilemma, the prisoners find themselves wondering whether the other prisoner will cooperate and remain silent, or decide to betray in the hopes of walking free.

If a prisoner assumes that the partner is trustworthy and will remain silent, speaking up is the best response in terms of self preservation, because there is a chance of walking. The prisoner might also assume that the partner has come to the same conclusion, in which case speaking up to avoid an even longer prison sentence becomes vital, and both prisoners lose out.

Many people use the prisoner's dilemma to show how situations can escalate through a series of seemingly rational options. For example, people stuck in dense traffic often choose to take selfish actions in the hopes of getting ahead, rather than cooperating with the collective. As a result, gridlock often emerges, with everyone losing in the situation.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@Spacedancer: The prisoner's dilemma is "a concept in game theory". The author of this article is not talking about two actual prisoners who have been arrested by police officer's in a modern 1st world country. It's supposed to be a simplified method of testing how two people will try to guess each other's next action without being able to see what the other one is doing, or know what they are thinking.

The different values that are brought in, or the consequences of taking different actions based on the actions of the other party, create the variables and pressures that makes the game apply to real world situations, such as the grid lock. The game does not take into account the interviewers, but simply focuses on the 'prisoners' or rather, the participants in the game.


Regarding a prison assuming a partner is trustworthy, etc.: This is not entirely true.

In the prisoner's dilemma and in all police matters, the police routinely lie to the prisoners. If the prisoners know this, it changes the dynamic.

The article suggests only a cynical view to the dilemma. If both prisoners trust each other and refuse to talk, the premise put forth must allow that in the case of weak evidence they both will walk.

In real life situations, a fair amount of the time the police don't have enough to convict either prisoner, which is why they use the prisoner's dilemma in the first place. Therefore, it is not necessarily a zero sum game.

Mutual shared goals and a strong bond of trust can result in a "win win" situation for the prisoners. The police are relying on the prisoners base instincts of fear, coupled with self preservation.

The real life percentage of the option I posit occurring may be low. This, however, can be explained by the fact that generally, the probability of people who commit crimes to be strongly trusting of each other is also low. They are likely to have trust issues in general. Big ones.

I propose an alternative situation: prisoners of war. If unit cohesion, training, and the soldiers' personal sense of honor are high, it is more likely that no one will talk i.e. "name, rank and serial number". There is no reason to believe giving truthful information will benefit any single individual since there is no reason to trust the captors in the first place, and soldiers fully understand that it will certainly harm the common goal: defeating the enemy. This flips the dilemma on its head.

In the final graph, cooperation in the automobile gridlock situation is put forth as the metaphor. This example posits many people who don't know or care about each other. In the prisoner's dilemma the issue of trust and mutual goals must be accepted as a viable strategy.

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