The honour of parents is a fair and noble treasure to their posterity, but to have the use of a treasure of wealth and honour, and to leave none to your successors, because you have neither money nor reputation of your own, is alike base and dishonourable.

The science [geometry] is pursued for the sake of the knowledge of what eternally exists, and not of what comes for a moment into existence, and then perishes.

Better a good enemy than a bad friend.

And first he will see the shadows best, next the reflections of men and other objects in the water, and then the objects themselves, then he will gaze upon the light of the moon and the stars and the spangled heaven...Last of all he will be able to see the sun.

He who advises a sick man, whose manner of life is prejudicial to health, is clearly bound first of all to change his patient's manner of life.

Any man may easily do harm, but not every man can do good to another.

Boys should abstain from all use of wine until their eighteenth year, for it is wrong to add fire to fire.