 It was twenty years later, however, before his magnum opus, The Idea of God in the Light of Recent Philosophy appeared. This book began life as Gifford Lectures delivered at the University of Aberdeen in the years 1912 and 1913. World War I (in which Seth's son Ronald fought and died) delayed both their revision and their publication. Consequently, they were not published until 1917. Lecture One begins with David Hume's Dialogues Concerning Natural Religion, and taking that as his starting point, Seth proceeds to address all the issues that had long dominated philosophical debate in Scotland. These include the existence of God, the relation of mind to body, the nature and scope of science, the theory of knowledge and the problem of skepticism. The 'recent philosophy', to which the subtitle refers, is the division and debate between empirical psychology and idealistic philosophy that had taken up competing sides on these questions. The heart of Seth's strategy is to analyze the defects of of empiricism and Idealism, and then to seek an integration of the compelling philosophical insights of both. He acknowledges that the Scottish philosophical tradition is inherently naturalistic, while at the same time accepting the Idealists rejection of Hume's narrow empiricism. In Lecture V of the first series, Seth accordingly elaborates and defends what he calls 'higher' naturalism. Three elements are key to this more sophisticated version of the naturalism that united Hume and Reid. First, philosophy has to be grounded in experience. It relies on both introspection and experiment, and cannot proceed satisfactorily in the form of rationalistic deductions from a priori principles. Second, dispassionately considered, we experience different orders of mind. The mind of animals is different to the mind of human beings. In particular, the human mind exhibits moral consciousness, something wholly lacking in other creatures. This is no less a fact of experience than anything biological observation or laboratory experiments might reveal. Given these critical differences between the kinds of mind experienced in nature, it is a mistake to seek to bring all evolved creatures within the scope of a unitary causal or biological explanation. Thirdly, the perennial task of philosophy is to search for a comprehensive explanation of experience. Philosophy's proper ambition is not to be a distinctive science, but to formulate an explanatory understanding that will integrate the radical differences within experience without eliminating them. Both psychologism and Idealism, whatever other merits they may have, fail in this respect.