Central to the Rawls–Harsanyi dispute is the question of whether the core modeling device of Rawls' theory of justice, the original position, justifies Rawls' principles of justice, as Rawls suggests, or whether it justifies the average utility principle, as Harsanyi suggests. Many commentators agree with Harsanyi and consider this dispute to be primarily about the correct application of normative decision theory to Rawls' original position. I argue that, if adequately conceived, the Rawls–Harsanyi dispute is not primarily a dispute about the correct application of normative decision theory to Rawls' original position. Instead, Rawls and Harsanyi aim to model different moral ideals, and this difference in their moral assumptions leads them to significantly different conclusions about justice. There is no winner in the Rawls–Harsanyi dispute. Instead, the dispute merely clarifies the moral ideals and their formal representations that need to be assumed in order to justify either Rawls' contractualist principles of justice or the average utility principle. Thus understood, the Rawls–Harsanyi dispute offers a promising starting point for future research that can deepen and enrich our understanding of the demands of justice.

It is argued that the Nash bargaining solution cannot serve as a principle of distributive justice because (i) it cannot secure stable cooperation in repeated interactions and (ii) it cannot capture our moral intuitions concerning distributive questions. In this article, I propose a solution to the first problem by amending the Nash bargaining solution so that it can maintain stable cooperation among rational bargainers. I call the resulting principle the stabilized Nash bargaining solution. The principle defends justice in the form 'each according to her basic needs and above this level according to her relative bargaining power'. In response to the second problem, I argue that the stabilized Nash bargaining solution can serve as a principle of distributive justice in certain situations where moral reasoning is reduced to instrumental reasoning. In particular, I argue that rational individuals would choose the stabilized Nash bargaining solution in Rawls' original position.

In this article, I derive a weak version of Kant's categorical imperative within an informal game-theoretic framework. More specifically, I argue that Hobbesian agents would choose what I call the weak principle of universalization, if they had to decide on a rule of conflict resolution in an idealized but empirically defensible hypothetical decision situation. The discussion clarifies (i) the rationality requirements imposed on agents, (ii) the empirical conditions assumed to warrant the conclusion, and (iii) the political institutions that are necessary to implement the derived principle. The analysis demonstrates the moral significance of the weak principle of universalization and its epistemic advantage over the categorical imperative.

In this article, I argue that if one closely follows Hobbes' line of reasoning in Leviathan, in particular his distinction between the second and the third law of nature, and the logic of his contractarian theory, then Hobbes' state of nature is best translated into the language of game theory by an assurance game, and not by a one-shot or iterated prisoner's dilemma game, nor by an assurance dilemma game. Further, I support Hobbes' conclusion that the sovereign must always punish the Foole, and even exclude her from the cooperative framework or take her life, if she defects once society is established, which is best expressed in the language of game theory by a grim strategy. That is, compared to existing game-theoretic interpretations of Hobbes, I argue that the sovereign plays a grim strategy with the citizens once society is established, and not the individuals with one another in the state of nature.

Harsanyi defends utilitarianism by means of an axiomatic proof and by what he calls the ‘equiprobability model’. Both justifications of utilitarianism aim to show that utilitarian ethics can be derived from Bayesian rationality and some weak moral constraints on the reasoning of rational agents. I argue that, from the perspective of Bayesian agents, one of these constraints, the impersonality constraint, is not weak at all if its meaning is made precise and that generally it even contradicts individual rational agency. Without the impersonality constraint, Harsanyi’s two justifications of utilitarianism on the grounds of Bayesian rationality fail. As an alternative, I develop a contractarian framework that is compatible with individual rational agency and Harsanyi’s central assumptions, and that allows the derivation of moral conclusions on the grounds of Bayesian rationality. The developed framework offers a novel justification of contractarian ethics and may best be described as a combined version of Harsanyi’s equiprobability model and Rawls’s original position.