On the Limits of the Human Mind
by Voltaire

SOMEONE asked Newton one day why he walked when he wanted to, and how his arm and his hand moved at his will. He answered manfully that he had no idea. " But at least," his interlocutor said to him, " you who understand so well the gravitation of the planets will tell me why they turn in one direction rather than in another! " And he again confessed that he had no idea.

Those who taught that the ocean was salt for fear that it might become putrid, and that the tides were made to bring our ships into port (The Abbe Pluche in " The Spectacle of Nature "), were somewhat ashamed when the reply was made to them that the Mediterranean has ports and no ebb. Musschenbroeck himself fell into this inadvertence.

Has anyone ever been able to say precisely how a log is changed on the hearth into burning carbon, and by what mechanism lime is kindled by fresh water? Is the first principle of the movement of the heart in animals properly understood? does one know clearly how generation is accomplished? has one guessed what gives us sensations, ideas, memory? We do not understand the essence of matter any more than the children who touch its surface.

Who will teach us by what mechanism this grain of wheat that we throw into the ground rises again to produce a pipe laden with an ear of corn, and how the same soil produces an apple at the top of this tree, and a chestnut on its neighbour? Many teachers have said-'' What do I not know? " Montaigne used to say " What do I know? "

Ruthlessly trenchant fellow, wordy pedagogue, meddlesome theorist, you seek the limits of your mind. They are at the end of your nose.