In addition to stating what the representatives think of the world and the results of their agreement for the case, there must also be a standard by which the representative parties can evaluate various contractual possibilities. They must be able to evaluate options based on their values, whatever they may be. Rawls models the parties to the contractual situation in such a way that, at least initially, they have only one measure of value: primary goods. They choose the notion of justice they do, believing that it is likely to produce the most important goods for them and their descendants. This specification of the evaluation parameter is consistent throughout the selection and, therefore, the choice in the original position can be modeled as the choice of a person. Since there is evaluative diversity between representatives, more complex matching models will be required (see § 3). As Rawls acknowledged in his 1958 essay “Justice as Fairness,” one way for the parties to resolve their disagreements is to use negotiated solutions as proposed by R.B. Braithwaite (1955). Rawls himself rejected negotiated solutions for the social contract, because in his view such solutions are based on threat advantages and “each according to his threat advantage is hardly a principle of equity” (Rawls 1958, 58n). Gauthier, however, followed this approach and built his morale by agreeing on the Kalai-Smorodinsky negotiated solution (see also Gaus 1990, chap. Binmore (2005) has recently developed a version of the social contract theory based on the Nash-negotiated solution, as has Ryan Muldoon (2017), while Moehler (in preparation) relies on a “stabilized” Nash negotiated solution. Gauthier has since adopted a less formal negotiating approach, but it is even closer to its initial solution than to the Nash solution (2013). In addition to Rawls` concern about the benefit of the threat, one drawback of all these approaches is the variety of negotiated solutions, which can differ significantly.
Although the Nash solution is the most popular today, it can have counterintuitive effects. In addition, many argue that negotiated solutions are inherently vague and that, therefore, the only way to reach a determination is to introduce unrealistic or controversial assumptions (Sugden, 1990, 1991). Similar problems also exist with balance selection in games (see Vanderschraaf 2005 and Harsanyi and Selten 1988). .