JACK and Jill have been arrested. The District Attorney now tells them this. They can either talk or keep silent. If they both talk, they will each get a ten-year sentence. If one of them talks (confessing for both) and the other does not, the one who talked will go free; the other will get a twenty-year sentence. If they both keep silent, each will get a one-year sentence on some trumped-up charge. The DA makes sure they believe him. Then he puts them in separate cells and goes to take their pleas.

Say that neither Jack nor Jill has any idea of what the other will do but that each supposes that it doesn't depend on what he (she) will do. Also that neither expects to meet the other again at some future time, or to meet the other's cousins in a dark alley somewhere. Also that neither cares at all about how the other makes out; each cares only about the length of his (her) own stay in jail. This lets each map his (her) own problem as in Figure 2.1.

Jack is here the row-chooser, Jill the column-chooser – S is staying silent, T is talking. Each number-pair refers to the outcome of one of the possible action-pairs, the first number being Jack's ranking of that outcome, the second being Jill's (the larger the number, the higher the ranking). The rankings reveal that talking is the dominant option for both: each would do better by talking, whatever the other did. So if Jack and Jill are both rational, both of them will talk.