McCosh's position was mainly in the tradition of Thomas Reid and other Scottish common-sense philosophers. He denied that our beliefs about the nature of the external world rest on causal or other inferences from perceptual ideas, but held that they are the direct accompaniments of sensation, and thus not open to question. He also argued for the a priori nature of fundamental principles such as those of causality and morality. Our judgements and other cognitions are regulated by such principles, though that is not to say that everyone is aware of them; they can be reached through reflection on our experience, when they are recognised as self-evidently necessary. In his moral theory, especially, McCosh differed from many of his contemporaries in being relatively uninfluenced by Kant.
Evolution
McCosh's most original work concerned the attempt to reconcile evolution and Christianity. In 1874, Charles Hodge, the theologian and intellectual leader at the Presbyterian Seminary in Princeton, published What is Darwinism?, claiming that Darwinism, was, in essence, atheism. To Hodge, Darwinism was contrary to the notion of design and was therefore clearly atheistic. Hodge's views determined the position of the Seminary until his death in 1878. Hodge simply refused to accept that natural laws alone could create complex organisms that fit into their niches so perfectly and that evolution could explain origins. While he didn't consider all evolutionary ideas to be in conflict with his religion, he was concerned with its teaching in colleges. Meanwhile at the college across town President John Maclean also rejected Darwin's theory of evolution. However in 1868, McCosh became president at the college. McCosh realized that much of Darwinism could and would be proved sound, and so he strove to prepare Christians for this event. Instead of conflict between science and religion, McCosh sought reconciliation. Insisting on the principle of design in nature, McCosh interpreted the Darwinian discoveries as more evidence of the prearrangement, skill, and purpose in the universe. He thus demonstrated that Darwinism was not atheistic nor in irreconcilable hostility to the Bible. McCosh thus argued that evolution, far from being inconsistent with belief in divine design, glorifies the divine designer. This aspect of his work found popularity among most Presbyterians clergy, who found his arguments useful in their attempts to cope with scientific philosophy. The Presbyterians in America thus could choose between two schools of thought on evolution, both based in Princeton. The Seminary held to Hodge's position until his supporters were ousted in 1929, and the college became a world class center of the new science of evolutionary biology. The debate between McCosh as president of the college and Charles Hodge, head of Princeton Seminary, during the late 1860s and 1870s exemplified the classic conflict between science and religion over the question of Darwin's evolution theory. McCosh offered the first public endorsement of evolution by an American religious leader. However, the two men showed greater similarities regarding matters of science and religion than popularly appreciated. Both supported the increasing role of scientific inquiry in natural history and resisted its intrusion into philosophy and religion. The debate vitalized the college.
Main works
An Examination of Mr J. S. Mill's Philosophy
Philosophical Papers containing "Examination of Sir W. Hamilton's Logic", "Reply to Mr Mill's third edition", and "Present State of Moral Philosophy in Britain".
