Here, then, are three classes of belief which in some shape or other common sense holds, has always held, and cannot help holding. But evidently the shapes in which they may be held are many. They vary from age to age and from person to person. They are modified by education, by temperament, by the general condition of learning, by individual opportunities, and by social pressure. The common sense of the twentieth century A.D. is very different from the common sense of the twentieth century B.C. Yet, different though it be, it possesses unalterable similarities, and up to a certain point submits to the same classification. If you desire an illustration, consider the case of matter, or of material things. All men believe in what is commonly called the “external world”—they believe in it with evidence, or without evidence, sometimes (like David Hume) in the teeth of evidence, in any case independently of evidence. But as to what this “external world” really is they differ profoundly. The expert of to-day differs from the expert of yesterday, both differ from the average man, the average man of the twentieth century differs from his predecessors, and they differ from each other according to the stage of general and scientific culture at which they have severally arrived. III But, though all this be granted, to what, you may be disposed to ask, does it lead? What has it got to do with Theism? It is not alleged that in any shape these inevitable beliefs are necessarily true; it is admitted that in most of the shapes in which men have held them they are actually false; it is not even suggested that a belief in God is to be counted among them. How, then, is Natural Theology advanced? To answer this question would be to anticipate the nine lectures which are still to come. In the meanwhile, it may be enough to say that these beliefs of common sense supply the material on which I propose to work; that I shall treat them as a developing and improving system, of which the present phase is the most developed and the best. It is with this phase that I am chiefly concerned. If, for example, I make use of beliefs about the “external world” they will be (mainly) the beliefs of contemporary or recent science so far as I know them. If I make use of ethics or æsthetics, it will be the ethics and æsthetics of Western civilisation, not of Melanesia. I shall not add to them nor subtract from them. I shall not criticise nor question them. I shall accept them at their face values. But I shall ask what this acceptance implies. I shall ask how these values are to be maintained. And in particular I shall inquire whether the course of development, whose last known stages these beliefs represent, can be regarded as a merely naturalistic process without doing fatal damage to their credit.