Rudolf Otto (1869-1937) was an eminent German Lutheran theologian, philosopher, and comparative religionist, who is regarded as one of the most influential scholars of religion in the early 20th century. He is best known for his theory of numinous, a profound emotional experience he argued was at the heart of the world's religions. Otto evntually came to conceive his work as part of a science of religion which was divided into the philosophy of religion, the history of religion, and the psychology of religion. His first book was Naturalism and Religion (1904) which divides the world ontologically into the mental and the physical, a position reflecting Cartesian dualism. He argues that consciousness cannot be explained in terms of physical or neural processes, further arguing that all knowledge of the physical world is mediated by personal experience. In his preface to this English translation of 1907 the Rev W D Morrison notes that Dr Otto possesses the rare merit of combining a high philosophic discipline with an accurate and comprehensive knowledge of the science of organic nature, allowing him to comment authoritatively on the debate concerning the religious and the non-religious conception of human life and destiny.