It is curious to imagine what would have been the effect of the life and the death of Socrates had he lived and died just as he did with one sole exception, that Plato and Xenophon had not been his disciples. Socrates wrote nothing: oral discourse was his sole instrument of teaching. When its last memories had faded away, we might have known as little of him as we really know of Pythagoras. He would still indeed have been the greatest of heathen names because he died for his moral convictions. This might have been all, and it would have been very much. This, however, was not to be. In Xenophon’s _Memorabilia_ we have an accurate life-portrait of the man, while in the great genius of Plato we have the application of what may be termed Socratic principles to the formation of an ethical, logical, and physical system. The Megaric(359) school of Euclides, and Phædo’s school of Elis, took indeed one side of his doctrine, the dialectic, for their special subject of inquiry; the Cynic school of Antisthenes and the Cyrenian school of Aristippus another side, the ethical: but it was Plato who embraced in one comprehensive scheme the whole grasp of his master’s thought, as well as the collective approved elements of former systems. The principle of Socrates concerning the union of knowledge and virtue invited his followers to work out a system of dialectics and ethics.(360) And further the dialectic process of induction and definition, which Aristotle tells us that Socrates introduced, was made by Plato the foundation of his philosophy.(361) Its central point is the doctrine of Ideas. Now the Platonic Idea is the object of the conception. As a single object becomes known by its representation, so the Idea becomes known by its conception. It is not the essence as such which dwells in many similar individual objects, but that essence as represented perfectly in its kind, unalterably, in unity, independence, and self-existence. The Idea points to the general, but is represented by Plato as an original image of the individual projected as it were outside of time and space. Conceive individuals which have a similar being, or belong to the same class, delivered from the limits of time and space, of materiality and individual imperfections, and so reduced to that unity which is the groundwork of their existence, and such unity is the Platonic Idea. The highest Idea is the Idea of the good,(362) which is as it were the sun in the realm of Ideas, viewed as the first cause of being and of knowledge. Plato seems to identify it with the highest godhead. Thus the method to attain the knowledge of Ideas is dialectics, which comprehend the double path of rising to the general and returning from the general to the particular.