The existent universe is a scale of being lying between the two extremes of formless matter and matterless form. But this must not be merely asserted, as a general {289} principle. It must be carried out in detail. The passage of matter into form must be shown in its various stages in the world of nature. To do this is the object of Aristotle's Physics, or philosophy of nature. If nature is to be understood, we must keep in mind certain general points of view. In the first place, since form includes end, the entire world-process, as passage of matter into form, is essentially movement towards ends. Everything in nature has its end and function. Nothing is purposeless. Nature seeks everywhere to attain the best possible. Everywhere we find evidences of design and of rational plan. Aristotle's philosophy of nature is essentially teleological. This does not, however, exclude the principle of mechanism, and to investigate mechanical causes is part of the duty of science. But mechanical causes turn out in the end to be teleological, because the true efficient cause is the final cause. But if nothing in nature is aimless or useless, this is not to be interpreted in a narrow anthropocentric spirit. It does not mean that everything exists for the use of man, that the sun was created to give him light by day, the moon by night, and that plants and animals exist only for his food. It is true that, in a certain sense, everything else sublunary is _for_ man. For man is the highest in the scale of beings in this terrestrial sphere, and therefore as the higher end, he includes all lower ends. But this does not exclude the fact that lower beings have each its own end. They exist for themselves and not for us.