The human mind is an evolutionary product, just like the human body.

If anything affects your eye, you hasten to have it removed; if anything affects your mind, you postpone the cure for a year.

What a torture to talk to filled heads that allow nothing from the outside to enter them.

Every thought is, strictly speaking, an afterthought.

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

It is far, far better and much safer to have a firm anchor in nonsense than to put out on the troubled seas of thought.

The sleep of reason produces monsters.

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

In psychoanalysis nothing is true except the exaggerations.

What the brain does by itself is infinitely more fascinating and complex than any response it can make to chemical stimulation.

Not all heads have a brain.

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

The mind is not, I know, a highway but a temple, and its doors should not be carelessly left open.