‘Cambridge idealism’ – the phrase sounds like a mischievous verbal paradox. Idealism, as Richter has accustomed us to suppose, set the tone of late nineteenth-century Oxford; while contemporary Cambridge, Lord Annan teaches, preserved a tradition of empirical rationalism. At Balliol Green and Toynbee evolved a ‘secular religion’ from the metaphysics of Hegel and Kant; at Cambridge Sidgwick and Marshall embarked upon a rationalist revision of utilitarianism, developing (for the most part) suggestions incompletely worked out by Mill. Green and Toynbee were idealists; Sidgwick and Marshall were rationalists: the differences between the philosophic systems thery constructed seem crystal clear. Yet the contrast can be exaggerated. Whether their fundamental premiss was the principle of utility or the conviction that ‘the Universe is a single, eternal activity or energy, of which it is the essence to be self-conscious, that is, to be itself and not-itself,’ Oxford idealists and Cambridge rationalists were both preoccupied by contemporary social problems, both formulated essentially social philosophies concerned with the right conduct of individuals in their relations with others, and both arrived at comparable policy prescriptions at almost exactly the same time.