It being our determination to discourse of Natural Philosophy, we judge it necessary, in the first place and chiefly, to divide the body of philosophy into its proper members, so that we may know what is that which is called philosophy, and what part of it is physical, or the explanation of natural things. The Stoics affirm that wisdom is the knowledge of things human and divine; that philosophy is the pursuit of that art which is convenient to this knowledge; that virtue is the sole and sovereign art which is thus convenient; and this distributes itself into three general parts—natural, moral, and logical. By which just reason (they say) philosophy is tripartite; of which one natural, the other moral, the third logical. The natural when our inquiries are concerning the world and all things contained in it; the ethical is the employment of our minds in those things which concern the manners of man's life; the logical (which they also call dialectical) regulates our conversation with others in speaking. Aristotle, Theophrastus, and after them almost all the Peripatetics give the same division of philosophy. It is absolutely requisite that the complete person he contemplator of things which have a being, and the practiser of those thing which are decent; and this easily appears by the following instances. If the question be proposed, whether the sun, which is so conspicuous to us, be informed of a soul or inanimate, he that makes this disquisition is the thinking man; for he proceeds no farther than to consider the nature of that thing which is proposed. Likewise, if the question be propounded, whether the world be infinite, or whether beyond the system of this world there is any real being, all these things are the objects about which the understanding of man is conversant.

But if these be the questions,—what measures must be taken to compose the well-ordered life of man, what are the best methods to govern and educate children, or what are the exact rules whereby sovereigns may command and establish laws,—all these queries are proposed for the sole end of action, and the man skilled therein is the moral and practical man.