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

The moral decisions of others should be treated with respect, as long as such decisions do not conflict with the principle of tolerance.

Almost everyone... seems to be quite sure that the differences between the methodologies of history and of the natural sciences are vast. For, we are assured, it is well known that in the natural sciences we start from observation and proceed by induction to theory. And is it not obvious that in history we proceed very differently? Yes, I agree that we proceed very differently. But we do so in the natural sciences as well.

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

Criticism of my alleged views was widespread and highly successful. I have yet to meet a criticism of my views.

We have become makers of our fate when we have ceased to pose as its prophets.

In so far as a scientific statement speaks about reality, it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality.