1. The prisoners dilemma

2. The situation
• Imagine …
– You live in a totalitarian regime where opposition to the
government is repressed.
– Walking home from work you are arrested and
immediately taken to a police station for interrogation.
– You are accused of plotting, with a man called Smith, to
overthrow the government.
– You profess your innocence and maintain that you don’t
know Smith. However it soon becomes clear to you that
the regime is more interested in extracting a confession
than in the truth.
– You are very scared.
– The chief interrogator offers you a deal:

3. The deal
• If Smith doesn’t confess, but you confess against him,
they will release you. You’ll go free, whereas Smith,
who did not cooperate, will be put away for 10 years.
• If Smith confesses and you don’t, the situation will be
reversed – he will go free while you get 10 years.
• If you both confess, you will be each sentenced to 5
years.
• If neither of you confess, there won’t be enough
evidence to convict either of you. They can hold you
for a year; but then they’ll have to let you go.

4. The dilemma
WHAT SHOULD YOU DO?
CONFESS OR NOT CONFESS?

5. Remember to the deal
• If Smith doesn’t confess, but you confess against him,
they will release you. You’ll go free, whereas Smith,
who did not cooperate, will be put away for 10 years.
• If Smith confesses and you don’t, the situation will be
reversed – he will go free while you get 10 years.
• If you both confess, you will be each sentenced to 5
years.
• If neither of you confess, there won’t be enough
evidence to convict either of you. They can hold you
for a year; but then they’ll have to let you go.

6. Why you should confess.
• Either Smith will confess or he won’t.
• Suppose Smith confesses. The, if you confess
you’ll get 5 years, whereas if you don’t confess
you’ll get 10 years. Therefore, if he confesses
you’re better off confessing.
• Suppose Smith doesn’t confess. Then: if you
confess you’ll go free; if you don’t confess you’ll
spend a year in prison. So if he doesn’t confess,
you’re still better off.
• So you must confess – it’ll get you out of jail the
quickest.

7. But …
• Smith is being offered the same deal.
• Therefore, following his logic (the same logic
as yours), he will confess.
• So you’ll both get 5 years.
• But if you had both done the opposite, each of
you would have got out of prison in only 1
year.

8. So …
• By rationally pursuing your own interests you
will both end up worse off than if you’d acted
differently.
• If you simultaneously do what is not in your
best interests, you will both be better off.