He has long given up the notion that virtue cannot be taught; and he is disposed to modify the thesis of the Protagoras, that the virtues are one and not many. He is not unwilling to admit the sensible world into his scheme of truth. Nor does he assert in the Republic the involuntariness of vice, which is maintained by him in the Timaeus, Sophist, and Laws (Protag., Apol., Gorg.). Nor do the so-called Platonic ideas recovered from a former state of existence affect his theory of mental improvement. Still we observe in him the remains of the old Socratic doctrine, that true knowledge must be elicited from within, and is to be sought for in ideas, not in particulars of sense. Education, as he says, will implant a principle of intelligence which is better than ten thousand eyes. The paradox that the virtues are one, and the kindred notion that all virtue is knowledge, are not entirely renounced; the first is seen in the supremacy given to justice over the rest; the second in the tendency to absorb the moral virtues in the intellectual, and to centre all goodness in the contemplation of the idea of good. The world of sense is still depreciated and identified with opinion, though admitted to be a shadow of the true. In the Republic he is evidently impressed with the conviction that vice arises chiefly from ignorance and may be cured by education; the multitude are hardly to be deemed responsible for what they do. A faint allusion to the doctrine of reminiscence occurs in the Tenth Book; but Plato’s views of education have no more real connection with a previous state of existence than our own; he only proposes to elicit from the mind that which is there already. Education is represented by him, not as the filling of a vessel, but as the turning the eye of the soul towards the light.