Philosophy is formally defined by Hobbes as knowledge of effects from causes and causes from effects by means of legitimate rational inference. This implies the equal validity of the deductive and inductive methods,--while Bacon had proclaimed the latter the most important instrument of knowledge,--as well as the exclusion of theology based on revelation from the domain of science. Philosophy is objectively defined as the theory of body and motion: _all that exists is body; all that occurs, motion_. Everything real is corporeal; this holds of points, lines, and surfaces, which as the limits of body cannot be incorporeal, as well as of the mind and of God. The mind is merely a (for the senses too) refined body, or, as it is stated in another place, a movement in certain parts of the organic body. All events, even internal events, the feelings and passions, are movements of material parts. "Endeavor" is a diminutive motion, as the atom is the smallest of bodies; sensation and representation are changes in the perceiving body. Space is the idea of an existing thing as such, _i. e_., merely as existing outside the perceiving subject; time, the idea of motion. All phenomena are corporeal motions, which take place with mechanical necessity. Neither formal nor final causes exist, but only efficient causes. All that happens takes its origin in the activity of an external cause, and not in itself; a body at rest (or in motion) remains at rest (or in motion) forever, unless affected by another in a contrary sense. And as bodies and their changes constitute the only objects of philosophy, so the mathematical method is the only correct method. There are two kinds of bodies: natural bodies, which man finds in nature, and artificial bodies, which he himself produces. By the latter Hobbes refers especially to the state as a human artefact. Man stands between the two as the most perfect natural body and an element in the political body. Philosophy, therefore, besides the introductory _philosophia prima_, which discusses the underlying concepts, consists of three parts: physics, anthropology, and politics. Even the theory of the state is capable of demonstrative treatment; moral phenomena are as subject to the law of mechanical causation as physical phenomena.