“For a scientist, altering your doctrines when the facts change is not a sign of weakness.”

“The word 'God' is for me nothing more than the expression and product of human weaknesses, the Bible a collection of honorable, but still primitive legends which are nevertheless pretty childish. No interpretation, no matter how subtle, can (for me) change this.”

“Weakness of attitude becomes weakness of character.”

“One cannot alter a condition with the same mind set that created it in the first place.”

“The true sign of intelligence is not knowledge but imagination.”

“I cannot conceive of a great scientist without this profound faith: Science without religion is lame, religion without science is blind.”

“I fully agree with you about the significance and educational value of methodology as well as history and philosophy of science. So many people today - and even professional scientists - seem to me like somebody who has seen thousands of trees but has never seen a forest. A knowledge of the historic and philosophical background gives that kind of independence from prejudices of his generation from which most scientists are suffering. This independence created by philosophical insight is - in my opinion - the mark of distinction between a mere artisan or specialist and a real seeker after truth.[Correspondance to Robert Thorton in 1944]”