And all knowledge, when separated from justice and virtue, is seen to be cunning and not wisdom; wherefore make this your first and last and constant and all-absorbing aim, to exceed, if possible, not only us but all your ancestors in virtue; and know that to excel you in virtue only brings us shame, but that to be excelled by you is a source of happiness to us.

Books are immortal sons deifying their sires.

Arithmetic is a kind of knowledge in which the best natures should be trained, and which must not be given up.

Knowledge is true opinion.

Arguments derived from probabilities are idle.

There are three arts which are concerned with all things: one which uses, another which makes, and a third which imitates them.

Vision, in my view, is the cause of the greatest benefit to us, inasmuch as none of the accounts now given concerning the Universe would ever have been given if men had not seen the stars or the sun or the heavens. But as it is, the vision of day and night and of months and circling years has created the art of number and has given us not only the notion of Time but also means of research into the nature of the Universe. From these we have procured Philosophy in all its range, than which no greater boon ever has come or will come, by divine bestowal, unto the race of mortals.