It can't happen here is always wrong: a dictatorship can happen anywhere.

It is wrong to ask who will rule. The ability to vote a bad government out of office is enough. That is democracy.

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

The growth of our knowledge is the result of a process closely resembling what Darwin called 'natural selection'; that is, the natural selection of hypotheses: our knowledge consists, at every moment, of those hypotheses which have shown their (comparative) fitness by surviving so far in their struggle for existence, a competitive struggle which eliminates those hypotheses which are unfit.

In point of fact, no conclusive disproof of a theory can ever be produced; for it is always possible to say that the experimental results are not reliable or that the discrepancies which are asserted to exist between the experimental results and the theory are only apparent and that they will disappear with the advance of our understanding. If you insist on strict proof (or strict disproof) in the empirical sciences, you will never benefit from experience, and never learn from it how wrong you are.

No book can ever be finished. While working on it we learn just enough to find it immature the moment we turn away from it

We hate the very idea that our own ideas may be mistaken, so we cling dogmatically to our conjectures.