Study without desire spoils the memory, and it retains nothing that it takes in.

Though I may not . . . be able to quote other authors, I shall rely on that which is much greater and more worthy - on experience.

The variety of colour in objects cannot be discerned at a great distance, excepting in those parts which are directly lighted up by the solar rays.

He who loves practice without theory is like the sailor who boards ship without a rudder and compass and never knows where he may cast.

He who wishes to see how the soul inhabits the body should look to see how that body uses its daily surroundings. If the dwelling is dirty and neglected, the body will be kept by its soul in the same condition, dirty and neglected.

Every action done by nature is done in the shortest way.

We must doubt the certainty of everything which passes through the senses, but how much more ought we to doubt things contrary to the senses, such as the existence of God and the soul.