He who seeks for methods without having a definite problem in mind seeks in the most part in vain.

As long as a branch of science offers an abundance of problems, so long it is alive; a lack of problems foreshadows extinction or the cessation of independent development.

However unapproachable these problems may seem to us and however helpless we stand before them, we have, nevertheless, the firm conviction that their solution must follow by a finite number of purely logical processes.

Physics is much too hard for physicists.

The infinite! No other question has ever moved so profoundly the spirit of man.

One can measure the importance of a scientific work by the number of earlier publications rendered superfluous by it

One must be able to say at all times--instead of points, straight lines, and planes--tables, chairs, and beer mugs