Tim Van Gelder's blog put me on to some interesting philosophical arguments mapped in ReasonAble, the forerunner to Rationale software, by Dave Spurret of the University of Durban.

I have an interest in game-theory, so the argument maps for the contention that it is rational to defect in a one shot prisoner's dilemma drew my attention:

(Click to enlarge)

For those who are unfamiliar with the prisoners dilemma, the wikipedia entry is a good introduction:

In game theory, the prisoner's dilemma is a type of non-zero-sum game in which two players can "cooperate" with or "defect" (i.e. betray) the other player. In this game, as in all game theory, the only concern of each individual player ("prisoner") is maximizing his/her own payoff, without any concern for the other player's payoff.

The argument that it is always better to defect (in a single iteration game) is based upon the premise that:

In the classic form of this game, cooperating is strictly dominated by defecting, so that the only possible equilibrium for the game is for all players to defect. In simpler terms, no matter what the other player does, one player will always gain a greater payoff by playing defect. Since in any situation playing defect is more beneficial than cooperating, all rational players will play defect.

This can also be illustrated by use of a simple table:

From this table you can see that if a player Co-operates, then the otcome for that player is guaranteed to be either *Win *or *Lose-big*. In contrast, if the player Defects, the guaranteed outcome for that player is either *Win-big *or *Lose*. No matter what the other player does, it is in each player's interest to defect.