The reduction of all phenomena by Democritus to a _mechanics of atoms_ was theoretically an enrichment of physics, for it anticipated the underlying principle of modern physics. The apparent qualities of things and the qualitative changes of things are conceived by Democritus to be in truth only a quantitative relation of atoms. He set before himself the task of explaining in detail how this or that quality consists of atoms in mechanical motion. The mental life of man must be explained in the same way. So too, wherever he could, he emphasized more sharply than his predecessors the mechanical necessity of the movement of atoms. Impact caused by contact of the atoms was the cause of every occurrence and change. No event is to be explained as the manifestation of some spirit, or referred to some spiritual agency. Mechanical cause is behind every event; mechanical cause is the unifying principle of the doctrine of Democritus; mechanical cause is the reason for the chasm between the philosophy of Plato, of Aristotle, and that of Democritus. It is the reason, too, why the theory of Democritus was obscured until modern times. All teleological conceptions and all hylozoistic and animistic ideas are expelled from the theory of Democritus, on the assumption that spatial form and motion are simpler and more comprehensible terms of explanation. Thus for the first time we have a conscious _outspoken materialism_, and for the first time the world is conceived to be a _universal reign of mechanical law_.