=The Kinds of Bodies.= There are two kinds of bodies, natural and artificial. Natural bodies are those belonging to the physical world. The artificial bodies are the institutions of society, of which the most important is the State. Man belongs to both classes of bodies――he has a physical nature and he is a member of the State. Man is the connecting link between natural and artificial bodies. Philosophy is therefore divided into three parts: _physics_, which treats of purely natural bodies; _psychology_, which treats of man in his rôle as a natural individual; _politics_, which treats of man in social congregations with his fellows. Looking at the situation from the other end, political bodies are decomposable into men, men are in turn decomposable into physical bodies. Political bodies are dependent on the psychical nature of men, and the psychical nature of men is dependent on the nature of physical bodies, _i. e._ on bodies and their motions. Thus all bodies, natural and artificial, must be explained in terms of motion, if they are explained scientifically. Physical bodies are the first term leading up through man to the last term in the series, which is the State. =Hobbes’s Application of the Mathematical Theory to Psychology.= Although the prime interest of Hobbes lay in the political life of man, he nevertheless made an original contribution to psychology. He snatched the science of mental phenomena from the hands of the scholastic theologian and made it for the first time an independent science. Psychology had been based upon the assumptions of the theologian; for these Hobbes substituted the assumptions of the mathematician. Consciousness became in his hands not a soul, but the motion of bodies. It is described by him as “the movement of certain parts of the organic body.” The states of consciousness, such as sensations, perceptions, etc., are brain movements or the refined movements of atoms in the nervous system. Memory and imagination are “decaying sensations”; thought is the sum of several sensations; experience is the totality of sensations bound together by the rigid laws of association. Hobbes was the father of what is known as the Associational Psychology, or the theory that consciousness is composed of mental atoms under fixed laws of association.