When you know a thing, to hold that you know it; and when you do not know a thing. To allow that you do not know it—this is knowledge.

To furnish the means of acquiring knowledge is the greatest benefit that can be conferred upon mankind. It prolongs life itself and enlarges the sphere of human existence.

The desire of power in excess caused the angels to fall; the desire of knowledge in excess caused man to fall.

No one can draw more out of things, books included, than he already knows. A man has no ears for that to which experience has given him no access.

Knowing your own darkness is the best method for dealing with the darknesses of other people.

He who has so little knowledge of human natures as to seek happiness by changing anything but his own disposition will waste his life in fruitless efforts.

Three passions, simple but overwhelmingly strong, have governed my life: the longing for love, the search for knowledge, and unbearable pity for the suffering of mankind.

Opinion is the medium between knowledge and ignorance.