If there is such a thing as natural theology, that is, a knowledge of a God or gods acquired by our natural faculties alone without the aid of a special revelation, it follows that it must be obtained by one or other of the methods by which all our natural knowledge is conveyed to us. Roughly speaking, these methods are two in number, namely, intuition and experience. Now if we ask ourselves, Do we know God intuitively in the same sense in which we know intuitively our own sensations and the simplest truths of mathematics, I think most men will acknowledge that they do not. It is true that according to Berkeley the world exists only as it is perceived, and that our perceptions of it are produced by the immediate action of God on our minds, so that everything we perceive might be described, if not as an idea in the mind of the deity, at least as a direct emanation from him. On this theory we might in a sense be said to have an immediate knowledge of God. But Berkeley's theory has found little acceptance, so far as I know, even among philosophers; and even if we regarded it as true, we should still have to admit that the knowledge of God implied by it is inferential rather than intuitive in the strict sense of the word: we infer God to be the cause of our perceptions rather than identify him with the perceptions themselves. On the whole, then, I conclude that man, or at all events the ordinary man, has, properly speaking, no immediate or intuitive knowledge of God, and that, if he obtains, without the aid of revelation, any knowledge of him at all, it can only be through the other natural channel of knowledge, that is, through experience.
The nature of experience.
In experience, as distinct from intuition, we reach our conclusions not directly through simple contemplation of the particular sensations, emotions, or ideas of which we are at the moment conscious, but indirectly by calling up before the imagination and comparing with each other our memories of a variety of sensations, emotions, or ideas of which we have been conscious in the past, and by selecting or abstracting from the mental images so compared the points in which they resemble each other. The points of resemblance thus selected or abstracted from a number of particulars compose what we call an abstract or general idea, and from a comparison of such abstract or general ideas with each other we arrive at general conclusions, which define the relations of the ideas to each other. Experience in general consists in the whole body of conclusions thus deduced from a comparison of all the particular sensations, emotions, and ideas which make up the conscious life of the individual. Hence in order to constitute experience the mind has to perform a more or less complex series of operations, which are commonly referred to certain mental faculties, such as memory, imagination, and judgment. This analysis of experience does not pretend to be philosophically complete or exact; but perhaps it is sufficiently accurate for the purpose of these lectures, the scope of which is not philosophical but historical.
Two kinds of experience, the experience of our own mind and the experience of an external world.
Now experience in the widest sense of the word may be conveniently distinguished into two sorts, the experience of our own mind and the experience of an external world. The distinction is indeed, like the others with which I am dealing at present, rather practically useful than theoretically sound; certainly it would not be granted by all philosophers, for many of them have held that we neither have nor with our present faculties can possibly attain to any immediate knowledge or perception of an external world, we merely infer its existence from our own sensations, which are as strictly a part of our mind as the ideas and emotions of our waking life or the visions of sleep. According to them, the existence of matter or of an external world is, so far as we are concerned, merely an hypothesis devised to explain the order of our sensations; it never has been perceived by any man, woman, or child who ever lived on earth; we have and can have no immediate knowledge or perception of anything but the states and operations of our own mind. On this theory what we call the world, with all its supposed infinitudes of space and time, its systems of suns and planets, its seemingly endless forms of inorganic matter and organic life, shrivels up, on a close inspection, into a fleeting, a momentary figment of thought. It is like one of those glass baubles, iridescent with a thousand varied and delicate hues, which a single touch suffices to shatter into dust. The philosopher, like the sorcerer, has but to wave his magic wand,
"And, like the baseless fabric of this vision,
The cloud-capped towers, the gorgeous palaces,
The solemn temples, the great globe itself,
Yea, all which it inherit, shall dissolve
And, like this insubstantial pageant faded,