The supernatural was an intellectual preoccupation for Scottish philosopher, theologian and later President of Princeton University James McCosh (1811-94), who attacked John Stuart Mill's 1843 System of Logic (also reissued in this series) for not addressing the issue of the supernatural. In this work, published in 1862, McCosh gives his full attention to the question, saying his aim was to 'disentangle the confusion' about the relationship between the natural and supernatural. He defines the supernatural as anything acting outside the sphere of nature. The first part of the book examines the natural world's relationship to the supernatural through a discussion of the laws and principles that are thought to govern nature. The second part takes the opposite approach, considering the relationship of the supernatural to the natural by examining instances within Christian literature, such as prophecy and miracles, which are difficult to explain.

The Scottish scholar James McCosh (1811-94) was a champion of the Free church, a successful and much-published philosophy professor at Belfast for 16 years, and an energetic and innovative President of Princeton University from 1868 to 1888. The Religious Aspect of Evolution was published in 1888, and this second edition from 1890 took account of A. R. Wallace's latest work, Darwinism (1889, also reissued in this series). McCosh, who already in Ireland had developed a 'theory of the universe conditioned by Christian revelation' was one of very few clergymen in America who defended evolutionary theory. He impressed upon his students that while there seemed to be great truth in Darwin's theory, the work of the coming age must be to separate that truth from the error springing up around it. This would enable scholars to follow and even embrace science while also retaining their faith in the Bible.