The sleep of reason produces monsters.

The brain is an unreliable organ, it is monstrously great, monstrously developed. Swollen, like a goiter.

What is outside my mind means nothing to it.

What is the hardest task in the world? To think.

“I think, therefore I am” is the statement of an intellectual who underrates toothaches.

Your mind’s got to eat, too.

Imagination is the secret and marrow of civilization. It is the very eye of faith.

Understanding is a very dull occupation.

A mind lively and at ease can do with seeing nothing, and can see nothing that does not answer.

Sooner or later if the activity of the mind is restricted anywhere, it will cease to function even where it is allowed to be free.

The brain may be regarded as a kind of parasite of the organism, a pensioner, as it were, who dwells with the body.

Madness need not be all breakdown. It may also be breakthrough.

The universe is an object of thought at least as much as it is a means of satisfying needs.