No particular theory may ever be regarded as absolutely certain.... No scientific theory is sacrosanct.

We have become makers of our fate when we have ceased to pose as its prophets.

Evolution is not a fact. Evolution doesn't even qualify as a theory or as a hypothesis. It is a metaphysical research program, and it is not really testable science.

We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.

A rationalist is simply someone for whom it is more important to learn than to be proved right; someone who is willing to learn from others - not by simply taking over another's opinions, but by gladly allowing others to criticize his ideas and by gladly criticizing the ideas of others

True ignorance is not the absence of knowledge, but the refusal to acquire it.

It is not possible to write clearly enough to avoid being misrepresented by people who are sufficiently determined to do so.