Reason must approach nature in order to be taught by it. It must not, however, do so in the character of a pupil who listens to everything that the teacher chooses to say, but of an appointed judge who compels the witness to answer questions which he has himself formulated.

Thinking in pictures precedes thinking in words.

The busier we are, the more acutely we feel that we live, the more conscious we are of life.

It is precisely in knowing its limits that philosophy consists.

A single line in the Bible has consoled me more than all the books I ever read besides.

Natural science physics contains in itself synthetical judgments a priori, as principles. ... Space then is a necessary representation a priori, which serves for the foundation of all external intuitions.

In man (as the only rational creature on earth) those natural capacities which are directed to the use of his reason are to be fully developed only in the race, not in the individual.