Sidgwick’s dualism of the practical reason is the idea that since egoism and utilitarianism
aim both to have rational supremacy in our practical decisions, whenever they conflict
there is no stronger reason to follow the dictates of either view. The dualism leaves us
with a practical problem: in conflict cases, we cannot be guided by practical reason to
decide what all things considered we ought to do. There is an epistemic problem as well:
the conflict of egoism and utilitarianism shows that they cannot be both self-evident
principles. Only the existence of a just God could, for Sidgwick, prevent the conflict and
thus solve the dualism. The paper first explores in detail and rejects some reconstructions
of the dualism: a purely logical account, and accounts whereby egoism and utilitarianism
are principles of pro tanto reasons or of sufficient reasons. Then it proposes a better account,
in which egoism and utilitarianism are logically compatible and yet conflicting
principles of all things considered reason. The account is shown to fit with Sidgwick’s
view of the dualism and of its practical and epistemic pitfalls. Finally, some views are
discussed as to the wider positive significance of the dualism, regarded as a challenge to
the rational authority of morality, or as indicating the structural opposition of agentrelative
and agent-neutral reasons, or again as the imperfect yet amendable attempt at a
comprehensive pluralist theory of practical reasons.
