In the inaugural lecture, delivered at Glasgow University in 1888, Müller discusses at length Lord Gifford’s life and the bequest he left to institute the Gifford Lectures in Natural Theology, summarising the details outlined therein. Müller notes that Lord Gifford defined clearly in his will what he understood by ‘natural theology’ and, as he was very open to new scientific inquiry, those subjects he wished to be examined in these lectures. Müller identifies the foundation of the Gifford lectureship as a very important sign of the times in the late nineteenth century with regard to the changing tides in philosophy, law, the physical and human sciences, the arts and even morality. In the second lecture on the ‘Definition of Religion’, Müller offers etymological, historical and dogmatic definitions of religion. He distinguishes between religion and theology, referring especially to Friedrich Schleiermacher’s definition, and between dogmatic and practical religion, concluding that religion has a double meaning, operating either as ‘belief’ or as a body of doctrines. Lecture III, ‘Examination of Definitions’, involves the extensive definition of Müller’s key terms and topics: natural and revealed religion, comparative theology, the object of religion, practical and theoretical religion; and discusses many key thinkers as well: Fichte, Goethe, Lavater, Kant, Caird, Pfleiderer, Martineau, Schenkel, Newman, Lotze, Mill, and Spinoza. In Europe, Christianity and Judaism were considered to be supernatural and revealed, as opposed to all other religions, which were ‘natural’ and hence not the product of divine revelation. Furthermore, most philosophers, in attempting to define religion theoretically, reduced it to sentiment or knowledge, leading to such different and even contradictory definitions as Schleiermacher’s (absolute dependence) and Hegel’s (absolute freedom). In Lecture IV, Müller examines the most significant definitions of religion (Wundt, Feuerbach, Gruppe, Niebuhr), showing that some philosophers emphasized the practical or theoretical character of religion while others promoted the idea that the true essence of religion was neither practical nor theoretical but rather a complete change in human nature through loving devotion to a Supreme Being. He also attends to definitions of and names for religion in other languages and cultures. Müller finally suggests his own definition of religion in Lecture V: for Müller, a true definition must account for the historical continuity of all religions; it ‘ought therefore to be applicable, not only to what religion is now, but to what religion was in its origin, and in its earliest developments’ (p. 104). Müller then defines religion as the experience or perception of the Infinite, a definition he slightly modifies later, fearing it is too broad.

In Lecture VI, ‘The Infinite in Nature, in Man, and in the Self’, Müller discusses these three manifestations of the Infinite, asserting that it was the initial perception of the Infinite that gave birth to the religious idea. The natural world discloses religious truth, and the study of our own nature can lead to a philosophical religion based on a perception of our true self and its relation to the Universal Self. In the seventh lecture, Müller explains the dissimilarity between religion and science, despite their shared concern for the Infinite. The Infinite lies beyond the horizon of our sensuous perception and cannot be fully and finally approached by science; ergo, science finds in religion its own raison d’etre. He then poses a fuller and final definition of his subject: ‘Religion consists in the perception of the infinite under such manifestations as are able to influence the moral character of man’ (p. 188). Müller examines ‘The Historical Method’ in Lecture VIII, championing the former as superior to other methods in the study of religion and the science of language. ‘The Historical Treatment of Religious Questions’ is the topic of Lecture IX, wherein Müller explains that ‘the burning question of the day is not what religion has been, or how it came to be what it is. The real question is the possibility of any religion at all, whether natural or supernatural’ (p. 221). He examines the agnosticism and atheism of his day alongside various philosophical treatments of the question, concluding that it is only by a historical study of these questions that one may become familiar with the ‘old problems of the philosophy of religion’, equipping us to face them again in their modern form. Lecture X, ‘Comparative Study of Religious Problems’, asserts that the historical study of religion is essential to the philosophy of religion, and Lecture XI evaluates the materials available for studying the growth and decay of natural religion, dividing these materials into four classes: language, myth, customs and laws and sacred texts.