All our thoughts and concepts are called up by sense-experiences and have a meaning only in reference to these sense-experiences. On the other hand, however, they are products of the spontaneous activity of our minds; they are thus in no wise logical consequences of the contents of these sense-experiences. If, therefore, we wish to grasp the essence of a complex of abstract notions we must for the one part investigate the mutual relationships between the concepts and the assertions made about them; for the other, we must investigate how they are related to the experiences.

I have not eaten enough of the tree of knowledge, though in my profession I am obligated to feed on it regularly.

The fairest thing we can experience is the mysterious. It is the fundamental emotion that stands at the cradle of true art and true science. It is the source of all true art and science. He who knows it not and can no longer wonder, no longer feel amazement, is as good as dead, a snuffed-out candle.

One must shy away from questionable undertakings, even when they bear a high-sounding name.

What can the schools do to defend democracy? Should they preach a specific political doctrine? I believe they should not. If they are able to teach young people to have a critical mind and a socially oriented attitude, they will have done all that is necessary.

The intuitive mind is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift.

I admit that thoughts influence the body.