In The Evolution of Religion, vol. 1, Caird establishes the continuum of the science and evolution of religion and endeavours to show that the definition or idea of religion cannot be found in any element common to all religions, of which the author discusses both objective and subjective types. In addition to summarizing views of subjective and objective religion, Caird discusses the moral strength of subjective religion and the opposition of the spirit to nature. He also addresses the transition from a national to a universal religion as well as the rise of moral individualism.
- Edward Caird