The prisoner's dilemma is a classic illustration of why rational people don't always cooperate--even when it's in their best interest to do so. In this episode of Instant Egghead, Scientific American editor Michael Moyer explains how it works.

6 Comments

1. 1. scribblerlarry 03:50 PM 11/11/12

   If that kind of silly "deal" worked, the cops would have a much better conviction rate and would not, as is almost always the case, need to beat confessions our of suspects.
   
   Whether or not the suspects act rationally, you, in thinking this a "dilemma" for them, have assumed that they haven't considered such a possibility long before they robbed the bank. They don't, at this late date, need to confer with each other. They will both refuse to co-operate and happily do the 30 days (which will, in fact, only be about 6 days).

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2. 2. geojellyroll 07:00 PM 11/11/12

   Logical in the scenario but too simplistic in the real world. In the 'real' world there are rarely isolated scenarios because there is not a finite subset of variables or shades of outcome.
   
   The last statement on nuclear deterrent for example...it implies that status quo is a goal...it's not. There was other 'stuff' happening.

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3. 3. marclevesque 07:05 PM 11/11/12

   "The prisoner's dilemma is a classic illustration of why rational people don't always cooperate--even when it's in their best interest to do so."
   
   How can that statement be cogent when the players don't have the option to cooperate.

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4. 4. GekokujoRhythm 10:12 AM 11/12/12

   Dear SciAm,
   Great video explanation.
   Here's some interesting information for everyone. While classical game theory does hold that individual's are inherently self-interested, and that the more rational course of action is to defect. What is really interesting is that when the PD is run experimentally that close to half the participants act irrationally and cooperate (Citation provided below for those interested in reading further).
   
   It would seem that reality, in this case, doesn't hold with theory.
   
   So, the question then becomes; Are we to assume that people are inherently irrational, or, rather, should we refine our conception of what is rational?
   
   1) Sally, David. Conversation and Cooperation in Social Dilemmas: A Meta-Analysis of Experiments from 1958 to 1992, Rationality and Society January 1995 7: 58-92.

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5. 5. Colin den Ronden 10:21 PM 3/11/13

   In the real world, suspects who have wisened up from 'bush lawyers' advice the previous time they have been in jail know what to do. Get separate lawyers so that each lawyer will blame the other suspect and create reasonable doubt. I think there is a case in France where identical twins are suspects in a rape case but the police don't know which one to charge. As for superpositions in thought, Hegel showed how you can do that. Hold a thesis and its contradictory antithesis in your head, and with enough thinking about it you one day may be able to come up with a synthesis. I have two contradictory thoughts in my head; 1. I believe that if an entity had enough intelligence it would be able to deduce the laws of the universe from first principles (black box thinking). 2. It is just about impossible to use your imagination if you have not experienced and experimented with the world i.e. some things you cannot conceive of because we are so dependent on the world to provide conceptions (denial of black box thinking). Being able to hold contradictory thoughts in your head can be an aid to thinking. For example, in some circumstances emotional arguments are just as valid as logical arguments, especially when it comes to human life. The abortion debate is unresolved because one side holds an emotional argument, while the other seeks to hold a purely logical argument.

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6. 6. scribblerlarry 02:05 AM 3/12/13

   The "Prisoners Dilemma" has two very different aspects to it. It can be looked at as merely a philosophical dilemma where one is asked to determine the most rational course of action by each of the prisoners. As an exercise in rational thinking it is just that - an exercise.
   
   But the second aspect of this situation is that it may take place in real life. Once it is being looked at from this position we find that many other considerations come into play.
   
   If the two accused were merely casual acquaintances, such as those formed by drug users who meet and are both bereft of funds for obtaining drugs, then both the cops and the lawyers will have no trouble convincing each to 'give up' the other.
   
   But that is not always the case. There are times when personal loyalty enters into the equation. Old lags who have co-operated on a number of 'jobs' in the past or who served time together or who have any of a number of reasons to be loyal to each other, will often not be amenable to any blandishments offered by the authorities.
   
   Also there is the factor of previous experience which has taught them that, once arrested, one says nothing - not one word - to the police. This is always the first advice of any competent lawyer. Saying anything at all is NEVER helpful and ALWAYS detrimental.
   
   Further, experienced criminals know very well that when the case goes to court it may be reported in great detail in the press. This means that if either or both talk, then they will be viewed as 'rats' by their fellow prisoners and subjected to jail-house punishment. The jail-house penalty for rats is often death.
   
   There are, of course, other considerations, but this few will show you how this dilemma is not, in real life, played out according to philosophic or 'apparently rational' rules.
   .

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