We do not choose political freedom because it promises us this or that. We choose it because it makes possible the only dignified form of human coexistence, the only form in which we can be fully responsible for ourselves. Whether we realize its possibilities depends on all kinds of things — and above all on ourselves.

With regards to political enemies Plato had a kill-and-banish principle. ... In interpreting it , modern-day Platonists are clearly disturbed by it, even as they make elaborate attempts to defend Plato.

Optimism is a duty. The future is open. It is not predetermined. No one can predict it, except by chance. We all contribute to determining it by what we do. We are all equally responsible for its success.

[To] interpret Parmenides as a Kant before Kant ... this is exactly what we must do.

Serious rational criticism is so rare that it should be encouraged. Being too ready to defend oneself is more dangerous than being too ready to admit a mistake.

I have learned more from Hayek than from any other living thinker, except perhaps Alfred Tarski - but not even excepting Russell.

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.