Of all forms of caution, caution in love is perhaps the most fatal to true happiness.
Change is scientific, progress is ethical; change is indubitable, whereas progress is a matter of controversy.
Freedom of opinion can only exist when the government thinks itself secure.
Men fear thought as they fear nothing else on earth -- more than ruin -- more even than death.... Thought is subversive and revolutionary, destructive and terrible, thought is merciless to privilege, established institutions, and comfortable habit. Thought looks into the pit of hell and is not afraid. Thought is great and swift and free, the light of the world, and the chief glory of man.
One of the symptoms of an approaching nervous breakdown is the belief that one's work is terribly important.
One should respect public opinion insofar as is necessary to avoid starvation and keep out of prison, but anything that goes beyond this is voluntary submission to an unnecessary tyranny.
The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts.
All exact science is dominated by the idea of approximation.
Three passions, simple but overwhelmingly strong, have governed my life: the longing for love, the search for knowledge, and unbearable pity for the suffering of mankind.
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it.