How fine nature’s habits may be, where repetition begins, and down to what depth a mathematical treatment can penetrate, is a question for the natural sciences to solve. Whether consciousness, for instance, accompanies vegetative life, or even all motion, is a point to be decided solely by empirical analogy. When the exact physical conditions of thought are discovered in man, we may infer how far thought is diffused through the universe, for it will be coextensive with the conditions it will have been shown to have. Now, in a very rough way, we know already what these conditions are. They are first the existence of an organic body and then its possession of adaptable instincts, of instincts that can be modified by experience. This capacity is what an observer calls intelligence; docility is the observable half of reason. When an animal winces at a blow and readjusts his pose, we say he feels; and we say he thinks when we see him brooding over his impressions, and find him launching into a new course of action after a silent decoction of his potential impulses. Conversely, when observation covers both the mental and the physical process, that is, in our own experience, we find that felt impulses, the conceived objects for which they make, and the values they determine are all correlated with animal instincts and external impressions. A desire is the inward sign of a physical proclivity to act, an image in sense is the sign in most cases of some material object in the environment and always, we may presume, of some cerebral change. The brain seems to simmer like a caldron in which all sorts of matters are perpetually transforming themselves into all sorts of shapes. When this cerebral reorganisation is pertinent to the external situation and renders the man, when he resumes action, more a master of his world, the accompanying thought is said to be practical; for it brings a consciousness of power and an earnest of success.