At the very outset, he disabused his class of the idea that moral philosophy was the same as mental philosophy. Moral philosophy was the science of ethics, the science of duty, and, in his view, it ought to embrace duty in all its relations, and to make use of all the light that could be brought to bear on that high theme. In particular--and here was the peculiar feature of his course--he desired to make the fullest use of what had been communicated on this subject by supernatural revelation. He justified this method of proceeding by an illustration. If natural philosophy were divided into two courses, and if one of them should relate to terrestrial objects and such parts of astronomy as might be prosecuted _without the telescope_, it would be strange indeed were the professor to make no allusion to that instrument, and to ignore, or even repudiate, all the light which it threw on the general scheme of things. So also, in investigating the science of ethics, it would be an extraordinary thing if no use were made of the Christian Revelation, supposing that its authenticity could be established as a revelation from heaven. Natural theology would form an important branch of his subject; but, in its very nature, natural theology was an incomplete and inadequate science. Following the light of nature, it proved the insufficiency of that light; it created the thirst and the longing for more light than it could itself supply. This further light revelation brought in. He held moral philosophy to be the study that ought immediately to precede that of theology; without theology it was incomplete. It would be no part of his course to set forth at full length the evidences for the Christian Revelation, but he would give a general view of them; he would show at least that there was a _prima facie_ presumption in favour of the divine origin of Christianity; and, therefore, that it was consistent with the principles of the Baconian philosophy to make use of its light in dealing with the great questions of moral obligation.
In fact, Chalmers in this matter took ground precisely opposite to that more recently taken by one of his countrymen--the munificent founder of the Gifford Lectures. According to Gifford, it becomes us to investigate the whole subject of natural theology and moral obligation without the slightest reference to any alleged supernatural revelation. This he held to be the sound, impartial, unprejudiced course of true philosophy, and the best way of attaining to simple, absolute truth. In the view of others, this is like the act of a man blindfolding himself before entering on a difficult investigation; or of a man walking in sparks of his own kindling, while, if he chose, he might be at work under the bright influence of electric light.
One might have thought that, after finishing his first course at St. Andrews, Chalmers would have held himself entitled to a long rest. But as soon as the session was ended, he set himself, during the fortnight that intervened, to prepare for the General Assembly. The question of pluralities, the question of pauperism, and the question of the amount of time to be spent by students in theological study were to be before the house, and Chalmers was interested in all. On one of these occasions he came into collision with Dr. Inglis, the leader of the Assembly; but, even on a point of order, Chalmers was equal to him, and in a division, he carried his motion. At the close of the Assembly, on the invitation of Mr. Leonard Horner, he took part in a meeting in Edinburgh on behalf of a then infant institution--the School of Arts. The motion which he made on that occasion was seconded by Sir Walter Scott. This was the only occasion on which these two eminent men appeared on the same platform and were associated in the same work.