Prisoner's Dilemma

Rules — Prisoner's Dilemma

• Each round you both choose at the same time and in secret: Stay silent (cooperate) or Snitch (defect).
• When both have chosen, the choices are revealed and each of you scores the points from the matrix shown on the board.
• Played round after round: scores accumulate. Whoever has more points at the end wins.
• The number of rounds is uncertain: from round 8 on, each round may be the last (🎲). You never know when it ends — so you can't just betray "on the final round".

Three scenarios

• Prisoner's Dilemma: snitching always pays more this round — yet if both snitch, both do worse than if both had stayed silent. The classic trap.
• Chicken: the disaster is mutual betrayal. Someone should yield… but who?
• Stag Hunt: cooperating together is the best outcome, but it only works if you trust each other.

How to play — a worked example

In the Prisoner's Dilemma scenario the points are (yours / rival's):

1. Round 1 — you both stay silent → +3 / +3. Score 3–3.
2. Round 2 — you snitch, rival stays silent → +5 / +0. Score 8–3.
3. Round 3 — now your rival snitches back. Both snitch → +1 / +1. Score 9–4.

The big idea

In a single round, snitching always scores more — so "rational" players both snitch and both get just +1, when they could have had +3 each. The magic of playing many rounds is that betrayal can be punished next time, so cooperation can pay off. Against the computer you are never told which strategy it plays: watch how it reacts to you and try to work it out. Pick Easy or Hard.