correction of human ideas was even more necessary than in our own times, because they were more bound up with words; and words when once presented to the mind exercised a greater power over thought. There is a natural realism which says, 'Can there be a word devoid of meaning, or an idea which is an idea of nothing?' In modern times mankind have often given too great importance to a word or idea. The philosophy of the ancients was still more in slavery to them, because they had not the experience of error, which would have placed them above the illusion. The method of the Parmenides may be compared with the process of purgation, which Bacon sought to introduce into philosophy. Plato is warning us against two sorts of 'Idols of the Den': first, his own Ideas, which he himself having created is unable to connect in any way with the external world; secondly, against two idols in particular, 'Unity' and 'Being,' which had grown up in the pre-Socratic philosophy, and were still standing in the way of all progress and development of thought. He does not say with Bacon, 'Let us make truth by experiment,' or 'From these vague and inexact notions let us turn to facts.' The time has not yet arrived for a purely inductive philosophy. The instruments of thought must first be forged, that they may be used hereafter by modern inquirers. How, while mankind were disputing about universals, could they classify phenomena? How could they investigate causes, when they had not as yet learned to distinguish between a cause and an end? How could they make any progress in the sciences without first arranging them? These are the deficiencies which Plato is seeking to supply in an age when knowledge was a shadow of a name only. In the earlier dialogues the Socratic conception of universals is illustrated by his genius; in the Phaedrus the nature of division is explained; in the Republic the law of contradiction and the unity of knowledge are asserted; in the later dialogues he is constantly engaged both with the theory and practice of classification. These were the 'new weapons,' as he terms them in the Philebus, which he was preparing for the use of some who, in after ages, would be found ready enough to disown their obligations to the great master, or rather, perhaps, would be incapable of understanding them.