[I would] rather discover one cause than gain the kingdom of Persia.

In fact we do not know anything infallibly, but only that which changes according to the condition of our body and of the [influences] that reach and impinge upon it.

There are two forms of knowledge, one genuine, one obscure. To the obscure belong all of the following: sight, hearing, smell, taste, feeling. The other form is the genuine, and is quite distinct from this. [And then distinguishing the genuine from the obscure, he continues:] Whenever the obscure [way of knowing] has reached the minimum sensibile of hearing, smell, taste, and touch, and when the investigation must be carried farther into that which is still finer, then arises the genuine way of knowing, which has a finer organ of thought.

[Democritus says:] By convention sweet is sweet, by convention bitter is bitter, by convention hot is hot, by convention cold is cold, by convention color is color. But in reality there are atoms and the void. That is, the objects of sense are supposed to be real and it is customary to regard them as such, but in truth they are not. Only the atoms and the void are real.

Of practical wisdom these are the three fruits: to deliberate well, to speak to the point, to do what is right.

He who intends to enjoy life should not be busy about many things, and in what he does should not undertake what exceeds his natural capacity. On the contrary, he should have himself so in hand that even when fortune comes his way, and is apparently ready to lead him on to higher things, he should put her aside and not o'erreach his powers. For a being of moderate size is safer than one that bulks too big.

If any one hearken with understanding to these sayings of mine many a deed worthy of a good man shall he perform and many a foolish deed be spared.

If one choose the goods of the soul, he chooses the diviner [portion]; if the goods of the body, the merely mortal.

'Tis well to restrain the wicked, and in any case not to join him in his wrong-doing.

'Tis not in strength of body nor in gold that men find happiness, but in uprightness and in fulness of understanding.

Not from fear but from a sense of duty refrain from your sins.

Repentance for one's evil deeds is the safeguard of life.

He who does wrong is more unhappy than he who suffers wrong.

'Tis a grievous thing to be subject to an inferior.

Many who have not learned wisdom live wisely, and many who do the basest deeds can make most learned speeches.

Fools learn wisdom through misfortune.

One should emulate works and deeds of virtue, not arguments about it.

Verily we know nothing. Truth is buried deep. (Another translation: "Of truth we know nothing, for truth is in a well." [http://www.perseus.tufts.edu/hopper/text?doc=Perseus:abo:tlg,0004,001:9:11 Diogenes Laertius, Lives of Eminent Philosophers R.D. Hicks, Ed.])

And yet it will be obvious that it is difficult to really know of what sort each thing is.

This argument too shows that in truth we know nothing about anything, but every man shares the generally prevailing opinion.

Men have fashioned an image of Chance as an excuse for their own stupidity. For Chance rarely conflicts with intelligence, and most things in life can be set in order by an intelligent sharpsightedness.

In a shared fish, there are no bones.

Education is an ornament for the prosperous, a refuge for the unfortunate.

Beautiful objects are wrought by study through effort, but ugly things are reaped automatically without toil.

The animal needing something knows how much it needs, the man does not.

Moderation multiplies pleasures, and increases pleasure.

The brave man is not only he who overcomes the enemy, but he who is stronger than pleasures. Some men are masters of cities, but are enslaved to women.

It is hard to fight desire; but to control it is the sign of a reasonable man.

The laws would not prevent each man from living according to his inclination, unless individuals harmed each other; for envy creates the beginning of strife.

To a wise man, the whole earth is open; for the native land of a good soul is the whole earth.

The man who is fortunate in his choice of son-in-law gains a son; the man unfortunate in his choice loses his daughter also.

If your desires are not great, a little will seem much to you; for small appetite makes poverty equivalent to wealth.

Disease of the home and of the life comes about in the same way as that of the body.

No power and no treasure can outweigh the extension of our knowledge.

Strength and beauty are the blessings of youth; temperance, however, is the flower of old age.

Man should know from this rule that he is cut off from truth.

Strength of body is nobility in beasts of burden, strength of character is nobility in men.

The hopes of the right-minded may be realized, those of fools are impossible.

The right-minded man, ever inclined to righteous and lawful deeds, is joyous day and night, and strong, and free from care. But if a man take no heed of the right, and leave undone the things he ought to do, then will the recollection of no one of all his transgressions bring him any joy, but only anxiety and self-reproaching.

Now as of old the gods give men all good things, excepting only those that are baneful and injurious and useless. These, now as of old, are not gifts of the gods: men stumble into them themselves because of their own blindness and folly.

Of all things the worst to teach the young is dalliance, for it is this that is the parent of those pleasures from which wickedness springs.

A sensible man takes pleasure in what he has instead of pining for what he has not.

A life without a holiday is like a long journey without an inn to rest at.

The pleasures that give most joy are the ones that most rarely come.

Throw moderation to the winds, and the greatest pleasures bring the greatest pains.

Men in their prayers beg the gods for health, not knowing that this is a thing they have in their own power. Through their incontinence undermining it, they themselves become, because of their passions, the betrayers of their own health.

Men achieve tranquillity through moderation in pleasure and through the symmetry of life. Want and superfluity are apt to upset them and to cause great perturbations in the soul. The souls that are rent by violent conflicts are neither stable nor tranquil. One should therefore set his mind upon the things that are within his power, and be content with his opportunities, nor let his memory dwell very long on the envied and admired of men, nor idly sit and dream of them. Rather, he should contemplate the lives of those who suffer hardship, and vividly bring to mind their sufferings, so that your own present situation may appear to you important and to be envied, and so that it may no longer be your portion to suffer torture in your soul by your longing for more. For he who admires those who have, and whom other men deem blest of fortune, and who spends all his time idly dreaming of them, will be forced to be always contriving some new device because of his [insatiable] desire, until he ends by doing some desperate deed forbidden by the laws. And therefore one ought not to desire other men's blessings, and one ought not to envy those who have more, but rather, comparing his life with that of those who fare worse, and laying to heart their sufferings, deem himself blest of fortune in that he lives and fares so much better than they. Holding fast to this saying you will pass your life in greater tranquillity and will avert not a few of the plagues of life—envy and jealousy and bitterness of mind.

All who delight in the pleasures of the belly, exceeding all measure in eating and drinking and love, find that the pleasures are brief and last but a short while—only so long as they are eating and drinking—but the pains that come after are many and endure. The longing for the same things keeps ever returning, and whenever the objects of one's desire are realized forthwith the pleasure vanishes, and one has no further use for them. The pleasure is brief, and once more the need for the same things returns.

We ought to regard the interests of the state as of far greater moment than all else, in order that they may be administered well; and we ought not to engage in eager rivalry in despite of equity, nor arrogate to ourselves any power contrary to the common welfare. For a state well administered is our greatest safeguard. In this all is summed up: When the state is in a healthy condition all things prosper; when it is corrupt, all things go to ruin.

The Greeks elaborated several theories of vision. According to the Pythagoreans, Democritus, and others vision is caused by the projection of particles from the object seen, into the pupil of the eye. On the other hand Empedocles, the Platonists, and Euclid held the strange doctrine of ocular beams, according to which the eye itself sends out something which causes sight as soon as it meets something else emanated by the object.