You live as if you were destined to live forever, no thought of your frailty ever enters your head, of how much time has already gone by you take no heed. You squander time as if you drew from a full and abundant supply, so all the while that day which you bestow on some person or thing is perhaps your last. You have all the fears of mortals and all the desires of immortals… What foolish forgetfulness of mortality to defer wise resolutions to the fiftieth or sixtieth year, and to intend to begin life at a point to which few have attained.

The philosopher forms his principles on an infinity of particular observations. He does not confuse truth with plausibility, he takes for truth what is true, for false what is false, for doubtful what is doubtful, and probable what is probable. The philosophical spirit is thus a spirit of observation and accuracy.

Passions destroy more prejudices than philosophy does.

There is only one virtue, justice; only one duty, to be happy; only one corollary, not to overvalue life and not to fear death.

Scepticism is the first step towards truth.

All things must be examined, debated, investigated without exception and without regard for anyone's feelings... We must run roughshod over all these ancient puerilities, overturn the barriers that reason never erected, give back to the arts and sciences the liberty that is so precious to them.

I have not the hope of being immortal, because the desire of it has not given me that vanity.