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.
The first factor in the cognitive process is an impression on a sense-organ, which, occasioned by external motion, continues onward to the heart and from this center gives rise to a reaction. The perception or sensation which thus arises is entirely subjective, a function of the knower merely, and in no way a copy of the external movement. The properties light, color, and sound, which we believe to be without us, are merely internal phenomena dependent on outer and inner motions, but with no resemblance to them. Memory consists in the lingering effects or residuary traces of perception; it is a sense or consciousness of having felt before (sentire se sensisse meminisse est), and ideas are distinguished from sensations as the perfect from the present tense. Experience is the totality of perceptions retained in memory, together with a certain foresight of the future after the analogy of the past. These stages of cognition, which can yield prudence but not necessary and universal knowledge, are present in animals as well as men. The human capacity for science is dependent on the faculty of speech; words are conventional signs to facilitate the retention and communication of ideas. As the memory-images denoted by words are weaker, fainter, and less clearly discriminated than the original sensations, it comes to pass that a number of similar ideas of memory receive a
