Definitions.... are never really needed, and rarely of any use

. . . it seems to me certain that more people are killed out of righteous stupidity than out of wickedness.

Our belief in any particular natural law cannot have a safer basis than our unsuccessful critical attempts to refute it.

Understanding a theory has, indeed, much in common with understanding a human personality. We may know or understand a man's system of dispositions pretty well; that is to say, we may be able to predict how he would act in a number of different situations. But since there are infinitely many possible situations, of infinite variety, a full understanding of a man's dispositions does not seem to be possible.

Historically speaking all - or very nearly all - scientific theories originate from myths.

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

It is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.