Whetstones are not themselves able to cut, but make iron sharp and capable of cutting.

Never hope to conceal any shameful thing which you have done; for even if you do conceal it from others, your own heart will know. … Pursue the enjoyments which are of good repute; for pleasure attended by honor is the best thing in the world, but pleasure without honor is the worst.

Those who directed the state in the time of Solon and Cleisthenes did not establish a polity which ... trained the citizens in such fashion that they looked upon insolence as democracy, lawlessness as liberty, impudence of speech as equality, and licence to do what they pleased as happiness, but rather a polity which detested and punished such men and by so doing made all the citizens better and wiser.

Be gracious to all men, but choose the best to be your friends.

Make no man your friend before inquiring how he has used his former friends; for you must expect him to treat you as he has treated them. Be slow to give your friendship, but when you have given it, strive to make it lasting; for it is as reprehensible to make many changes in one's associates as to have no friends at all. Neither test your friends to your own injury nor be willing to forego a test of your companions.

Spend your leisure time in cultivating an ear attentive to discourse, for in this way you will find that you learn with ease what others have found out with difficulty.

Oratory is good only if it has the qualities of fitness for the occasion, propriety of style, and originality of treatment, while in the case of letters there is no such need whatsoever.