Sidgwick considered Kant as one of his masters. However, he never devoted any
systematic attention to Kant’s ethical theory; moreover, in The Methods of Ethics he
concluded that Kantian ethics is inadequate to guide moral life. I review Sidgwick’s
references to Kant in order to show that – along with basic differences − there are
significant similarities in the main project of the two philosophers; and I suggest that,
should Sidgwick have deepened his understanding of Kant, he might have realised that
Kantian ethics offered a somewhat different way to accomplish the philosophical project
he was interested in, that is, the systematisation of the morality of common sense through
the establishment of certain moral axioms. I also suggest that Sidgwick’s
misunderstanding of the “formula of humanity” is at the heart of his final dismissal of
Kant’s ethics and that deepening his understanding of Kant might have led Sidgwick to
revise his views on the rationality of egoism, thereby opening the possibility to solve the
dualism of practical reason. Finally, I offer some speculations on the reasons why
Sidgwick never attempted a thorough confrontation with Kant, suggesting that both his
distaste for Kant’s metaphysics and his Millian utilitarian bias deterred him from it.
