In many multi-actor decision situations the parties involved do not share the same perception of rationality, the same basic values or the same information. This could be because the actors come from different cultural backgrounds (Thompson, 1984). Yet even quite culturally diverse actors can achieve agreement if they recognize their diversity, are willing to learn and exchange information, and agree on the legitimacy of some negotiation procedure or on some principles of fairness for use in mediation. These concepts seem difficult to formalize; yet, as shown later, formalization or abstraction is an important part of the cognition process, and thus necessary for a deeper understanding of the problem.