“Don't do anything that goes against your conscience, even if your country says so.”

“Never do anything against conscience, even if the state demands it.”

“Do not laugh at me for writing you without having anything sensible to say. But I am so enraged by the base manner in which the public is presently daring to concern itself with you that I absolutely must give vent to this feeling. I am impelled to tell you how much I have come to admire your intellect, your drive, and your honesty, and that I consider myself lucky to have made your personal acquaintance in Brussels. Anyone who does not number among these reptiles is certainly happy, now as before, that we have such personages among us as you, and Langevin too, real people with whom one feels privileged to be in contact. If the rabble continues to occupy itself with you, then simply don't read that hogwash, but rather leave it to the reptile for whom it has been fabricated.”

“The world is a dangerous place to live, not because of the people who are evil, but because of the people who don't do anything about it.”

“You do not really understand something unless you can explain it to your grandmother.”

“Do not worry about your difficulties in Mathematics. I can assure you mine are still greater.”

“Your imagination is your preview of life’s coming attractions.”