Nature, Man, and Self are the three great manifestations in which the infinite in some shape or other has been perceived, and every one of these perceptions has in its historical development contributed to what may be called religion. _Gifford Lectures, I._ Like all other experiences, our religious experience begins with the senses. Though the senses seem to deliver to us finite experiences only, many, if not all, of them can be shown to involve something beyond the Known, something unknown, something which I claim the liberty to call infinite. In this way the human mind was led to the recognition of undefined, infinite agents or agencies beyond, behind, and within our finite experience. The feelings of fear, awe, reverence, and love excited by the manifestations of some of these agents or powers began to react on the human mind, and thus produced what we call Natural Religion in its lowest and simplest form--fear, awe, reverence, and love of the gods. _Gifford Lectures, I._ The perception of the Infinite can be shown by historical evidence to be the one element shared in common by all religions. Only we must not forget that, like every other concept, that of the Infinite also had to pass through many phases in its historical evolution, beginning with the simple negation of what is finite, and the assertion of an invisible Beyond, and leading up to a perceptive belief in that most real Infinite in which we live and move and have our being. _Gifford Lectures, IV._ KNOWLEDGE The lesson that there are limits to our knowledge is an old lesson, but it has to be taught again and again. It was taught by Buddha, it was taught by Socrates, and it was taught for the last time in the most powerful manner by Kant. Philosophy has been called the knowledge of our knowledge; it might be called more truly the knowledge of our ignorance, or, to adopt the more moderate language of Kant, the knowledge of the limits of our knowledge. _Last Essays._ Metaphysical truth is wider than physical truth, and the new discoveries of physical observers, if they are to be more than merely contingent truths, must find their appointed place and natural refuge within the immovable limits traced by the metaphysician.... It is only after having mastered the principles of metaphysics that the student of nature can begin his work in the right spirit, knowing the horizon of human knowledge, and guided by principles as unchangeable as the pole star. _Last Essays._ There is no subject in the whole realm of human knowledge that cannot be rendered clear and intelligible, if we ourselves have perfectly mastered it. _Chips._