I ceased in the year 1764 to believe that one can convince one’s opponents with arguments printed in books. It is not to do that, therefore, that I have taken up my pen, but merely so as to annoy them, and to bestow strength and courage on those on our own side, and to make it known to the others that they have not convinced us.

One's first step in wisdom is to question everything - and one's last is to come to terms with everything.

Some people feel with their heads and think with their hearts.

I cannot say whether things will get better if we change; what I can say is they must change if they are to get better.

We now possess four principles of morality: 1) a philosophical: do good for its own sake, out of respect for the law; 2) a religious: do good because it is God's will, out of love of God; 3) a human: do good because it will promote your happiness, out of self-love; 4) a political: do good because it will promote the welfare of the society of which you are a part, out of love of society having regard to yourself. But is this not all one single principle, only viewed from different sides?

Nowadays three witty turns of phrase and a lie make a writer.

A good metaphor is something even the police should keep an eye on.