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!

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.

A thing is not proved because no one has ever questioned it... Skepticism is the first step toward truth.

For me, my thoughts are my prostitutes.

Those who fear the facts will forever try to discredit the fact-finders.

Only God and some few rare geniuses can keep forging ahead into novelty.

You risk just as much in being credulous as in being suspicious.