Allan Gibbard writes:
A chief task of moral philosophers is to discern such a rationale and to shape it by criticism and argument. Derek Parfit’s On What Matters looks to two great moral philosophers, Immanuel Kant in the late 18th century and Henry Sidgwick, whose treatise The Methods of Ethics first appeared in 1874. Kant, Parfit writes, ‘is the greatest moral philosopher since the ancient Greeks’, but Sidgwick’s Methods ‘is, I believe, the best book on ethics ever written’. Kant and Sidgwick are normally taken to stand for the two great opposing moral visions: Sidgwick for utilitarianism, which concerns itself with how to maximise happiness, and Kant for a moral law grounded in reason. Parfit finds, however, that Kant and Sidgwick are ‘climbing the same mountain’ by different routes. We are still far from the summit by either route, but as Parfit said a quarter-century ago, ‘compared with the other sciences, non-religious ethics is the youngest and the least advanced.’ As with any science, a mature ethics might take generations to formulate.