Language is made up of signs. According to what has just been said, natural signs are spontaneously produced by the play of the emotions. As a voluntary manifestation language is always artificial. The involuntary signs have been gradually divided into their component parts and simplified, while remaining intelligible. All artificial signs, says Comte, even in our species, spring from a voluntary “imitation” of the natural signs which are spontaneously produced. In this way both the formation and the interpretation of these signs are explained.[218] Hobbes used to define a sign as a constant relation between two phenomena, seen by the subject. The two phenomena are here a state of consciousness and a motion. Sometimes the state of consciousness determines the motion, sometimes the motion causes the reappearance of the state of consciousness. The institution of a system of signs is a means of “connecting the within with the without.” Language is thus for man a means of making the series of his intellectual states participate in the regularity which characterises external order. The logical function of language therefore springs from its very essence in which the phenomena of the objective world and the phenomena which belong to the feeling and thinking subject are joined. It is equivalent to a system for rendering the mental life objective.[219] Being thus made objective, these phenomena can henceforth be preserved and communicated, without man or the animals having had each an end in view, since the institution of the first signs is involuntary, and arises from “the combination between the muscular and nervous systems.” External order here acts as a regulator, even before thought has grasped it. The signs which are spontaneously produced are not all transformed into voluntary signs. Those which appeal to sight or to hearing present special advantages for this use, and as a matter of fact, the two classes of signs are concurrently used by the higher animals. Gestures and cries are the origin of what later becomes the system of artificial signs. By degrees, the communication of emotions gives way to the expression of thoughts. Among very civilised populations it even came to be believed that song had come from speech. But, on the contrary, speech came from song. To be convinced of this a glance at the animal world is sufficient. Up to this point the theory of language has been biological, and the acquired facts can thus be summed up: 1, Man does not express his thought in order to communicate it, but he communicates because he expresses it. 2, What is first expressed is emotion, not thought. By degrees language becomes intellectualized, as the mental life itself. 3, Expression is spontaneous and primary. It arises from the relation between the nervous and muscular systems. In the progressive transformation where, from being involuntary, the signs gradually become voluntary, they are at once causes and effects.