No rational argument will have a rational effect on a man who does not want to adopt a rational attitude.

Science does not rest upon solid bedrock. The bold structure of its theories rises, as it were, above a swamp. It is like a building erected on piles. The piles are driven down from above into the swamp, but not down to any natural or 'given' base; and if we stop driving the piles deeper, it is not because we have reached firm ground. We simply stop when we are satisfied that the piles are firm enough to carry the structure, at least for the time being.

It is a myth that the success of science in our time is mainly due to the huge amounts of money that have been spent on big machines. What really makes science grow is new ideas, including false ideas.

We all remember how many religious wars were fought for a religion of love and gentleness; how many bodies were burned alive with the genuinely kind intention of saving souls from the eternal fire of hell.

The history of science is everywhere speculative. It is a marvelous hiatory. It makes you proud to be a human being.

We must plan for freedom, and not only for security, if for no other reason than only freedom can make security more secure.

The moral decisions of others should be treated with respect, as long as such decisions do not conflict with the principle of tolerance.