The attempt to make heaven on earth invariably produces hell.

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.

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

A system such as classical mechanics may be 'scientific' to any degree you like; but those who uphold it dogmatically - believing, perhaps, that it is their business to defend such a successful system against criticism as long as it is not conclusively disproved - are adopting the very reverse of that critical attitude which in my view is the proper one for the scientist.

Genuine philosophical problems are always rooted outside philosophy and they die if these roots decay.

The history of science, like the history of all human ideas, is a history of irresponsible dreams, of obstinacy, and of error. But science is one of the very few human activities-perhaps the only one-in which errors are systematically criticized and fairly often, in time, corrected. This is why we can say that, in science, we often learn from our mistakes, and why we can speak clearly and sensibly about making progress there. In most other fields of human endeavour there is change, but rarely progress ... And in most fields we do not even know how to evaluate change.

I have insisted that we must be tolerant. But I also believe that this tolerance has its limits. We must not trust those anti-humanitarian religions which not only preach destruction but act accordingly. For if we tolerate them, then we become ourselves responsible for for their deeds.