Plotinus is a mystic, then, though not at all in the sense in which the term is often misused. He sets before his disciples a 'way of life' which leads by stages to the highest life of all, but that is just what Pythagoras and Plato had done, and it is only the continuation of a tradition which goes back among the Greeks to the sixth century B. C., nearly a thousand years before the time of Plotinus. His aim, like that of his predecessors, is the conversion of souls to this way of life, and he differs from such thinkers as the Stoics and the Epicureans in holding that the 'way of life' to which he calls them must be based once more on a systematic doctrine of God, the World and Man. The result was that the divorce which had existed for centuries between science and philosophy was once more annulled. We cannot say, indeed, that Plotinus himself made any special study of Mathematics, but there is no doubt at all that his followers did, and it is due to them, and especially to Proclus, that we know as much of Greek Mathematics as we do. Proclus was indeed the systematizer of the doctrine of Plotinus, though he differs from him on certain points, and his influence on later philosophy cannot be overestimated. It can be distinctly traced even in Descartes, whom it reached through a number of channels, the study of which has recently been undertaken by a French scholar, Professor Gilson, of the University of Strasbourg. When his researches are complete, the continuity of Greek and modern philosophy will be plainly seen, and the part played by Platonism in the making of the modern European mind will be made manifest. We shall then understand better than ever why Greek philosophy is a subject of perennial interest.