Only the real, rare, true scientific minds can endure doubt, which is attached to all our knowledge.

Men are more moral than they think and far more immoral than they can imagine.

Civilization is a process in the service of Eros, whose purpose is to combine single human individuals, and after that families, then races, peoples and nations, into one great unity, the unity of mankind. Why this has to happen, we do not know; the work of Eros is precisely this.

Cigars served me for precisely fifty years as protection and a weapon in the combat of life... I owe to the cigar a great intensification of my capacity to work and a facilitation of my self-control.

The impression forces itself upon one that men measure by false standards, that everyone seeks power, success, riches for himself, and admires others who attain them, while undervaluing the truly precious thing in life.

What progress we are making. In the Middle Ages they would have burned me. Now they are content with burning my books.

Religious doctrines … are all illusions, they do not admit of proof, and no one can be compelled to consider them as true or to believe in them.