No particular theory may ever be regarded as absolutely certain.... No scientific theory is sacrosanct.

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.

Historically speaking all - or very nearly all - scientific theories originate from myths.

The use of violence is justified only under a tyranny which makes reforms without violence impossible, and should have only one aim, that is, to bring about a state of affairs which makes reforms without violence possible.

Now this principle of induction cannot be a purely logical truth like a tautology or an analytic statement. . . .

No rational argument will have a rational effect on a man who does not want to adopt a rational attitude.

I don't know whether God exists or not. ... Some forms of atheism are arrogant and ignorant and should be rejected, but agnosticism—to admit that we don't know and to search—is all right. ... When I look at what I call the gift of life, I feel a gratitude which is in tune with some religious ideas of God. However, the moment I even speak of it, I am embarrassed that I may do something wrong to God in talking about God.