A fuzzy approach to the prisoner's dilemma.

The traditional iterated prisoner's dilemma (IPD) admits only two possible moves, cooperate (C) and defect (D), with no gradations involved. Nevertheless, when a rational agent perceives or implements a specific behavioral decision, it usually employs qualitative measures of the variables involved. In this paper, we propose an approach to the IPD where the possible moves are still confined to C and D, but these are no longer considered as two dichotomous choices, but as different attitudes that can have variable emphasis. The variables accounted for in the game are modeled as fuzzy sets, and the players' decisions are taken with the guidance of fuzzy expert systems. A computational tournament is performed, where in addition to the fuzzy players, the well-known successful strategists tit for tat (TFT) and Pavlov are also present. Some results are presented and briefly discussed. The main purpose of this paper is to investigate a model of the IPD in which the players' decisions are taken by means of a qualitative reasoning system.