For instance, on the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much - the wheel, New York, wars and so on - whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man - for precisely the same reasons.

The world is nothing, the man is all; in yourself is the law of all nature, and you know not yet how a globule of sap ascends; in yourself slumbers the whole of Reason; it is for you to know all, it is for you to dare all.

The heart has its reasons which reason knows nothing of.

Heroism feels and never reasons and therefore is always right.

The two principles of truth, reason and senses, are not only both not genuine, but are engaged in mutual deception. The senses deceive reason through false appearances, and the senses are disturbed by passions, which produce false impressions.

Man governs himself more by impulse than reason.

Our reason is always disappointed by the inconsistency of appearances.

For I am not so enamored of my own opinions that I disregard what others may think of them. I am aware that a philosopher's ideas are not subject to the judgement of ordinary persons, because it is his endeavor to seek the truth in all things, to the extent permitted to human reason by God. Yet I hold that completely erroneous views should be shunned. Those who know that the consensus of many centuries has sanctioned the conception that the earth remains at rest in the middle of the heaven as its centre would, I reflected, regard it as an insane pronouncement if I made the opposite assertion that the earth moves.

Those who are clever in imagination are far more pleased with themselves than prudent men could reasonably be.

Put the world's greatest philosopher on a plank that is wider than need be; if there is a precipe below, although his reason may convince him that he is safe, his imagination will prevail.

Nothing is so conformable to reason as to disavow reason.