Morals from rationality alone? Some doubts

Contractarians aim to derive moral principles from the dictates of instrumental rationality alone. It is well-known that contractarian moral theories struggle to identify normative principles that are both uniquely rational and morally compelling. Michael Moehler’s recent book, Minimal Morality, seeks to avoid these difficulties by developing a novel ‘two-level’ social contract theory, which restricts the scope of contractarian morality to cases of deep and persistent moral disagreement. Yet Moehler remains ambitious, arguing that a restricted version of Kant’s categorical imperative is a uniquely rational principle of conflict resolution. We develop a formal model of Moehler’s informal game-theoretic argument, which reconstructs a valid argument for Moehler’s conclusion. This model, in turn, enables us to expose how a successful argument for Moehler’s contractarian principle rests on assumptions that can only be justified by subtle yet significant departures from the standard conception of rationality. We thus extend our understanding of familiar contractarian difficulties by showing how they arise even if we restrict the scope of contractarian morality to a domain where its application seems both promising and necessary.