The distinction between ‘religious’ and secular thought is probably unreal and certainly difficult. The first half of the twentieth century seems, in retrospect, to fall, in this respect, into two contrasting periods—before 1914 and after 1918—the first characterised by a close relation between philosophy and religion, the second by a tendency to fall apart, influential philosophers holding that metaphysical statements are meaningless and theologians that Revelation needs no support from human reason. At the opening of the century Herbert Spencer was still alive and his agnostic theology of the ‘Unknowable’, which he derived from the Anglican Dean Mansel, was under fire from the rising school of Idealists. Positivism, of the Comtist type, was widely held as a philosophy which harmonised with the scientific outlook, and the proposition that the only genuine knowledge is scientific knowledge was widely accepted. About this time the word ‘Naturalism’ came into use as a general term for a scientific metaphysic which, with more or less emphasis, rejected the idea of God. Since this controversy on Naturalism was about the nature of truth and the limits of knowledge, it concerned many thinkers who would not have claimed to be theologians. The institution of the ‘Gifford Lectures’, which were explicitly devoted to the consideration of belief in God in the light of reason without resort to authority or alleged revelation, secured that the great themes of God, Freedom and Immortality were continually being examined from many points of view.