What makes our opponents useful is that they allow us to believe that without them we would be able to realize our goals.
It takes a very deep-rooted opinion to survive unexpressed.
The divine is perhaps that quality in man which permits him to endure the lack of God.
Take heed of critics even when they are not fair; resist them even when they are.
Whether man is disposed to yield to nature or to oppose her, he cannot do without a correct understanding of her language
It is sometimes important for science to know how to forget the things she is surest of.