Thinking in its lower grades, is comparable to paper money, and in its higher forms it is a kind of poetry.

The sun, the moon and the stars would have disappeared long ago... had they happened to be within the reach of predatory human hands.

Man lives by imagination.

What we call progress is the exchange of one nuisance for another nuisance.

There is nothing more fragile than civilization.

It is here [in mathematics] that the artist has the fullest scope of his imagination.

The mathematician has reached the highest rung on the ladder of human thought.