The development of intelligence in the modern world, as in Greece, has two sides: on the one hand, a working-free from the restrictions which theology or the State or other social authorities imposed; on the other hand, positive progress in knowledge of nature and of human life. Under its first aspect it is known as the growth of rationalism; under its second aspect, as the growth of science and education. We cannot separate the development into two periods, the one negative, the other positive, as was convenient in the case of Greece. The negative and the positive in the modern world have gone on contemporaneously, although the emphasis has sometimes been on one side and sometimes upon the other. We may, however, indicate three periods as standing out with clearly defined characteristics. (1) The Renaissance, in which the Greek spirit of scientific inquiry found a new birth; in which the discovery of new continents stimulated the imagination; and in which new and more fruitful methods of investigation were devised in mathematics and the natural sciences. (2) The period of the Enlightenment, in which the negative aspect of the process reached its sharpest definition. The doctrines of revealed religion and natural religion were criticised from the standpoint of reason. Mysteries and superstition were alike rejected. General intelligence made rapid progress. It was the "Age of Reason." (3) The Nineteenth Century, in which both the natural and social sciences underwent an extraordinary development. The doctrine of evolution has brought a new point of view for considering the organic world and human institutions. Education has come to be regarded as both the necessary condition for the safety of society and as the right of every human being; Science, in large measure set free from the need of fighting for its right to exist, is becoming constructive; it is assuming increasingly the duty of preserving human life and health, of utilizing and preserving natural resources, of directing political and economic affairs.