Front Page Titles (by Subject) MIND (LIMITS OF THE HUMAN). - The Works of Voltaire, Vol. VI (Philosophical Dictionary Part 4)
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MIND (LIMITS OF THE HUMAN). - Voltaire, The Works of Voltaire, Vol. VI (Philosophical Dictionary Part 4) 
The Works of Voltaire. A Contemporary Version. A Critique and Biography by John Morley, notes by Tobias Smollett, trans. William F. Fleming (New York: E.R. DuMont, 1901). In 21 vols. Vol. VI.
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MIND (LIMITS OF THE HUMAN).
Newton was one day asked why he stepped forward when he was so inclined; and from what cause his arm and his hand obeyed his will? He honestly replied, that he knew nothing about the matter. But at least, said they to him, you who are so well acquainted with the gravitation of planets, will tell us why they turn one way sooner than another? Newton still avowed his ignorance.
Those who teach that the ocean was salted for fear it should corrupt, and that the tides were created to conduct our ships into port, were a little ashamed when told that the Mediterranean has ports and no tide. Muschembrock himself has fallen into this error.
Who has ever been able to determine precisely how a billet of wood is changed into red-hot charcoal, and by what mechanism lime is heated by cold water?
The first motion of the heart in animals—is that accounted for? Has it been exactly discovered how the business of generation is arranged? Has any one divined the cause of sensation, ideas, and memory? We know no more of the essence of matter than the children who touch its superficies.
Who will instruct us in the mechanism by which the grain of corn, which we cast into the earth, disposes itself to produce a stalk surmounted with an ear; or why the sun produces an apple on one tree and a chestnut on the next to it? Many doctors have said: “What know I not?” Montaigne said: “What know I?”
Unbending decider! pedagogue in phrases! furred reasoner! thou inquirest after the limits of the human mind—they are at the end of thy nose.