Rationalism is an attitude of readiness to listen to contrary arguments and to learn from experience... of admitting that "I may be wrong and you may be right and, by an effort, we may get nearer the truth."

The attempt to make heaven on earth invariably produces hell.

Those who promise us paradise on earth never produced anything but a hell.

Man, some modern philosophers tell us, is alienated from his world: he is a stranger and afraid in a world he never made. Perhaps he is; yet so are animals, and even plants. They too were born, long ago, into a physico-chemical world, a world they never made.

[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.

Psychologism is, I believe, correct only in so far as it insists upon what may be called 'methodological individualism' as opposed to 'methodological collectivism'; it rightly insists that the 'behaviour' and the 'actions' of collectives, such as states or social groups, must be reduced to the behaviour and to the actions of human individuals. But the belief that the choice of such an individualist method implies the choice of a psychological method is mistaken.

We have the right not to tolerate the intolerant. We should tolerate even them whenever we can do so without running a great risk; but the risk may become so great that we cannot allow ourselves the luxury.