Denis Diderot

When superstition is allowed to perform the task of old age in dulling the human temperament, we can say goodbye to all excellence in poetry, in painting, and in music.

Reason is to the philosopher what grace is to the Christian.
Grace causes the Christian to act, reason the philosopher. Other men are carried away by their passions, their actions not being preceded by reflection: these are the men who walk in darkness. On the other hand, the philosopher, even in his passions, acts only after reflection; he walks in the dark, but by a torch.
The philosopher forms his principles from an infinity of particular observations. Most people adopt principles without thinking of the observations that have produced them, they believe the maxims exist, so to speak, by themselves. But the philosopher takes maxims from their source; he examines their origin; he knows their proper value, and he makes use of them only in so far as they suit him.
Truth is not for the philosopher a mistress who corrupts his imagination and whom he believes to be found everywhere; he contents himself with being able to unravel it where he can perceive it. He does not confound it with probability; he takes for true what is true, for false what is false, for doubtful what is doubtful, and probable what is only probable. He does more, and here you have a great perfection of the philosopher: when he has no reason by which to judge, he knows how to live in suspension of judgment...
The philosophical spirit is, then, a spirit of observation and exactness, which relates everything to true principles...

Watch out for the fellow who talks about putting things in order! Putting things in order always means getting other people under your control.

Only a very bad theologian would confuse the certainty that follows revelation with the truths that are revealed. They are entirely different things.

There is only one passion, the passion for happiness.

Happiest are the people who give most happiness to others.

Scepticism is the first step towards truth.

It has been said that love robs those who have it of their wit, and gives it to those who have none.

Superstition is more injurious to God than atheism.

We are all instruments endowed with feeling and memory. Our senses are so many strings that are struck by surrounding objects and that also frequently strike themselves.

The infant runs toward it with its eyes closed, the adult is stationary, the old man approaches it with his back turned.

In order to shake a hypothesis, it is sometimes not necessary to do anything more than push it as far as it will go.

To prove the Gospels by a miracle is to prove an absurdity by something contrary to nature.

The good of the people must be the great purpose of government. By the laws of nature and of reason, the governors are invested with power to that end. And the greatest good of the people is liberty. It is to the state what health is to the individual.

How old the world is! I walk between two eternities... What is my fleeting existence in comparison with that decaying rock, that valley digging its channel ever deeper, that forest that is tottering and those great masses above my head about to fall? I see the marble of tombs crumbling into dust; and yet I don’t want to die!

In any country where talent and virtue produce no advancement, money will be the national god. Its inhabitants will either have to possess money or make others believe that they do. Wealth will be the highest virtue, poverty the greatest vice. Those who have money will display it in every imaginable way. If their ostentation does not exceed their fortune, all will be well. But if their ostentation does exceed their fortune they will ruin themselves. In such a country, the greatest fortunes will vanish in the twinkling of an eye. Those who don't have money will ruin themselves with vain efforts to conceal their poverty. That is one kind of affluence: the outward sign of wealth for a small number, the mask of poverty for the majority, and a source of corruption for all.

Jacques said that his master said that everything good or evil we encounter here below was written on high.

Although a man may wear fine clothing, if he lives peacefully; and is good, self-possessed, has faith and is pure; and if he does not hurt any living being, he is a holy man.

The wisest among us is very lucky never to have met the woman, be she beautiful or ugly, intelligent or stupid, who could drive him crazy enough to be fit to be put into an asylum.

The decisions of law courts should never be printed: in the long run, they form a counterauthority to the law.