We never know what we are talking about.

Philosophy is a necessary activity because we, all of us, take a great number of things for granted, and many of these assumptions are of a philosophical character; we act on them in private life, in politics, in our work, and in every other sphere of our lives -- but while some of these assumptions are no doubt true, it is likely, that more are false and some are harmful. So the critical examination of our presuppositions -- which is a philosophical activity -- is morally as well as intellectually important.

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

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

Our aim must be to make our successive mistakes as quickly as possible. To speed up evolution.

[Great scientists] are men of bold ideas, but highly critical of their own ideas: they try to find whether their ideas are right by trying first to find whether they are not perhaps wrong. They work with bold conjectures and severe attempts at refuting their own conjectures.

I have come to the conclusion that Darwinism is not a testable scientific theory, but a metaphysical research programme.