The Prisoner's Dilemma
Suppose Nikkie and Bill are accused of collaborating on treasonous activity in a totalitarian society. The police put Nikkie and Bill in separate cells. Nikkie and Bill are not allowed to communicate with one another. Keep in mind that the police want t o get an admission of guilt from either Nikkie or Bill. Accordingly, the police offer Nikkie the following deal:
| Nikkie's Deal | Bill Confesses | Bill does not Confess | ||
| Nikkie Confesses | Nikkie gets 5 years | Bill gets 5 years | Nikkie gets 1 year | Bill gets 10 years |
| Nikkie does not Confess | Nikkie gets 10 years | Bill gets 1 year | Nikkie gets 2 years | Bill gets 2 years |
Leaving Nikkie to think it over, the police then go to Bill's cell and offer him the following deal:
| Bill's Deal | Nikkie Confesses | Nikkie does not Confess | ||
| Bill Confesses | Bill gets 5 years | Nikkie gets 5 years | Bill gets 1 year | Nikkie gets 10 years |
| Bill does not Confess | Bill gets 10 years | Nikkie gets 1 year | Bill gets 2 years | Nikkie gets 2 years |
You will note that the deals are constructed so as to provide a real incentive to Bill and Nikkie to confess. You will also note that the deals are identical: Nikkie and Bill are really being offered the same deal.
Now let us suppose that Nikkie and Bill are ordinary people who very much do not want to spend any time in jail. Let us also suppose that Nikkie and Bill are clear-thinking, reasonably intelligent individuals. How will they decide? Since they are rational, they argue as follows:
Nikkie's Reasoning
"All I know is that Bill will either confess or not. Accordingly,"
Suppose Bill confesses...
| 1 | If I confess, I will get 5 years. | ||
| 2 | If I don't confess, I will get 10 years. | ||
| ∴ | 3 | I should confess. | 1&2 |
Suppose Bill does not confess...
| 1 | If I confess, then I will get 1 year. | ||
| 2 | If I don't confess, then I will get 2 years. | ||
| ∴ | 3 | I should confess. | 1&2 |
Therefore: No matter what Bill does, I'm better off if I confess. So I should confess.
Bill's Reasoning
"All I know is that Nikkie will either confess or not. Accordingly,"
Suppose Nikkie confesses...
| 1 | If I confess, I will get 5 years. | ||
| 2 | If I don't confess, I will get 10 years. | ||
| ∴ | 3 | I should confess. | 1&2 |
Suppose Nikkie does not confess...
| 1 | If I confess, then I will get 1 year. | ||
| 2 | If I don't confess, then I will get 2 years. | ||
| ∴ | 3 | I should confess. | 1&2 |
Therefore: No matter what Nikkie does, I'm better off if I confess. So I should confess.
Reasoning carefully in their separate cells, Nikkie and Bill each conclude that they should confess. But then here is the dilemma. It seems clear that they should each confess by the above reasoning. But by both of them confessing, they each get 5 years . Had they each not confessed, they would have gotten only 2 years. What went wrong?
Really, nothing. That is why this is a dilemma. No error can be found in their reasoning. What is paradoxical is that by Nikkie and Bill doing what is in each of their best interests, they act contrary to their best interests. It is a remarkable result that Nikkie will be better off if she does what is not in her best interests and Bill will be better off if he does what is not in his best interests.
*Adapted from James Rachels, "The Elements of Moral Philosophy", 2nd ed. (McGraw Hill, 1993)