The history of scientific and technical discovery teaches us that the human race is poor in independent and creative imagination. Even when the external and scientific requirements for the birth of an idea have long been there, it generally needs an external stimulus to make it actually happen; man has, so to speak, to stumble right up against the thing before the idea comes.

A man must learn to understand the motives of human beings, their illusions, and their sufferings.

I cannot imagine a God who rewards and punishes the objects of his creation, whose purposes are modeled after our own -- a God, in short, who is but a reflection of human frailty. Neither can I believe that the individual survives the death of his body, although feeble souls harbor such thoughts through fear or ridiculous egotisms.

No idea is conceived in our mind independent of our five senses [i.e., no idea is divinely inspired].

The cult of individual personalities is always, in my view, unjustified. To be sure, nature distributes her gifts variously among her children. But there are plenty of the well-endowed ones too, thank God, and I am firmly convinced that most of them live quiet, unregarded lives.

[Asked about a book in which 100 Nazi professors charged him with scientific error.] Were I wrong, one professor would have been quite enough.

Where you see difficulty, I see opportunity.