The founder of the Atomist philosophy was Leucippus. Practically nothing is known of his life. The date of his birth, the date of his death, and his place of residence, are alike unknown, but it is believed that he was a contemporary of Empedocles and Anaxagoras. Democritus was a citizen of Abdera in Thrace. He was a man of the widest learning, as learning was understood in his day. A passion for knowledge and the possession of adequate means for the purpose, determined him to undertake extensive travels in order to acquire the wisdom and knowledge of other nations. He travelled largely in Egypt, also probably in Babylonia. The date of his death is unknown, but he certainly lived to a great age, estimated at from ninety to one hundred years. Exactly what were the respective contributions of Leucippus and Democritus to the Atomist philosophy, is also a matter of doubt. But it is believed that all the essentials of this philosophy were the work of Leucippus, and that Democritus applied and extended them, worked out details, and made the theory famous. Now we saw that the philosophy of Empedocles was based upon an attempt to reconcile the doctrine of Parmenides with the doctrine of Heracleitus. The {87} fundamental thought of Empedocles was that there is no absolute becoming in the strict sense, no passage of Being into not-being or not-being into Being. Yet the objects of the senses do, in some way, arise and pass away, and the only method by which this is capable of explanation is to suppose that objects, as whole objects, come to be and cease to be, but that the material particles of which they are composed are eternally existent. But the detailed development which Empedocles gave to this principle was by no means satisfactory. In the first place, if we hold that all objects are composed of parts, and that all becoming is due to the mixing and unmixing of pre-existent matter, we must have a theory of particles. And we do hear vaguely of physical particles in the doctrine of Empedocles, but no definition is given of their nature, and no clear conception is formed of their character. Secondly, the moving forces of Empedocles, Love and Hate, are fanciful and mythological. Lastly, though there are in Empedocles traces of the doctrine that the qualities of things depend on the position and arrangement of their particles, this idea is not consistently developed. For Empedocles there are only four ultimate kinds of matter, qualitatively distinguished. The differential qualities of all other kinds of matter must, therefore, be due to the mixing of these four elements. Thus the qualities of the four elements are ultimate and underived, but all other qualities must be founded upon the position and arrangement of particles of the four elements. This is the beginning of the mechanical explanation of quality. But to develop this theory fully and consistently, it should be shown, not merely that some qualities are ultimate and some {88}