It is difficult for the isolated individual to work himself out of the immaturity which has become almost natural for him.

Why were a few, or a single one, made at all, if only to exist in order to be made eternally miserable, which is infinitely worse than non-existence?

Human reason has the peculiar fate in one species of its cognitions that it is burdened with questions which it cannot dismiss, since they are given to it as problems by the nature of reason itself, but which it also cannot answer, since they transcend every capacity of human reason.

Great minds think for themselves.

Thinking in pictures precedes thinking in words.

Imagination is a powerful agent for creating, as it were, a second nature out of the material supplied to it by actual nature.

The instruction of children should aim gradually to combine knowing and doing. Among all sciences mathematics seems to be the only one of a kind to satisfy this aim most completely.