BERNARD WALLISER A SIMPLIFIED TAXONOMY OF 2x2 GAMES ABSTRACT. All 2 x 2 games are classified into eight configurations, following three natural criteria, and prototypes given for each, especially as concerns the Newcomb and chain-store paradoxes. Two pseudo-dynamic properties, move priority and dynamic inconsistency, arc examined in that framework, as well as more specifically, the problem of the origin of social institutions. Keywords: 2 x 2 games, taxonomy of games, Newcomb paradox, move priority, dynamic inconsistency. In various fields, original concepts or problems are often illustrated by standard examples like the prisoner's dilemma or the chicken game, taking the form of two-person games where each player has only two actions available. When preferences are ordinal and strict, it is possible to generate all of these games, classify them with some "natural" criteria, and specify the properties of the "folk games" due to the configuration where they take place. When preferences are ordinal and large, a lot of new games appear which frequently lay at the border of some preceding configurations, especially those associated with the Newcomb and chain- store paradoxes which can be generalized. The taxonomy can further be used to study some pseudo-dynamic properties like the priority of move problem, dynamic inconsistency and irreversibility, or even, when preferences are cardinal, dynamic problems such as the foundations of social institutions. 1. THE BASIC TAXONOMY Consider the set of all two-person games on normal form where each player (P' and P") has only two actions available (x~ and x~ for P'). Assume first the four possible issues being evaluated by each player with strict ordinal preferences; his utility index (u' and u") can then be defined as taking its value in the set /0, 1, 2, 3/. To normalize the games, it is Theory and Decision 25 (1988) 163-191. 9 1988 by Kluwer Academic Publishers.