Letter XIV

On Descartes and Newton

A Frenchman arriving in London finds things greatly changed in philosophy, as in everything else. He left the world full; he finds it empty. In Paris the universe is seen as composed of vortices of subtle matter; in London nothing of the kind is seen. Among us the pressure of the moon causes the sea's tides; among the English the sea gravitates toward the moon. Thus, when you think the moon ought to give us high tide, these gentlemen think there should be low tide—something which, unfortunately, cannot be verified, since to settle it one would have had to examine the moon and the tides at the first moment of creation.

You will also notice that the sun, which plays no part in this affair in France, contributes about a quarter to it here. Among our Cartesians everything happens through an impulse that we scarcely understand; with Mr. Newton it happens through an attraction whose cause is no better known. In Paris you picture the earth shaped like a melon; in London it is flattened on both sides. For a Cartesian, light exists in the air; for a Newtonian, it comes from the sun in six and a half minutes. Your chemistry performs all its operations with acids, alkalis, and subtle matter; attraction rules even English chemistry.

The very essence of things has changed completely. You agree neither on the definition of the soul nor on that of matter. Descartes assures us that the soul is the same thing as thought, and Locke makes a fairly good case to the contrary. Descartes further asserts that extension alone constitutes matter; Newton adds solidity.

These are serious disagreements.

It is not for me to settle such great quarrels between you.

The celebrated Newton, destroyer of the Cartesian system, died in the month of March in the year 1727. He lived honored by his countrymen and was buried like a king who had done good to his subjects. Here people eagerly read, and translated into English, the Eulogy of Mr. Newton delivered by Mr. de Fontenelle at the Academy of Sciences. In England they awaited his judgment as a solemn declaration of the superiority of English philosophy; but when they saw that he had not only erred in his account of that philosophy but had compared Descartes with Newton, the whole Royal Society of London rose up. Far from accepting the judgment, they sharply criticized the speech. Several, even—and these are not the most philosophical—were offended by the comparison simply because Descartes was French.

One must admit that these two great men differed greatly from each other in their conduct, their fortunes, and their philosophy.

Descartes was born with a brilliant and powerful imagination, which made him a singular man in private life as in his manner of reasoning. That imagination could not hide itself even in his philosophical works, where ingenious, dazzling comparisons appear at every turn. Nature had nearly made him a poet, and indeed he composed a verse entertainment for the queen of Sweden which, for the sake of his reputation, has not been printed.

He tried his hand at the profession of arms for a time, and later, having become a philosopher through and through, he did not think it beneath him to make love. By his mistress he had a daughter named Francine, who died young; he grieved deeply for her loss. Thus he experienced all that belongs to humanity.

For a long time he believed he needed to flee men, and above all his native country, to philosophize freely. He was right: the men of his time knew too little to enlighten him and were hardly capable of anything but doing him harm.

He left France because he was seeking truth, then persecuted there by the wretched philosophy of the schools; but he found no more reason in the universities of Holland, where he took refuge. For while in France the only propositions of his philosophy that were true were being condemned, he was also persecuted by the supposed philosophers of Holland, who understood him no better and, seeing his glory closer at hand, hated him all the more. He was forced to leave Utrecht; he endured an accusation of atheism, the last resort of slanderers; and he, who had employed all the acuity of his mind in seeking new proofs of God's existence, was suspected of not acknowledging a God at all.

So much persecution presupposed great merit and a brilliant reputation: indeed, he possessed both. Reason even broke through a little into the world, across the darkness of the schools and the prejudices of popular superstition. His name finally made so much noise that they sought to entice him to France with rewards. He was offered a pension of a thousand écus; he came in the hope of it, paid the fees for the patent, then sold at a price, received no pension, and went back to philosophize in his solitude in North Holland, at the very time when the great Galileo, at the age of eighty, languished in the prisons of the Inquisition for having demonstrated the motion of the earth.

At last he died in Stockholm, prematurely, as a result of an unhealthy regimen, surrounded by a few scholars who were his enemies and in the care of a physician who hated him.

The course of Sir Isaac Newton's life was entirely different: he lived nearly eighty-five years, always at peace, happy and honored in his native land. His great good fortune was to have been born not only in a free country but in an age when scholastic absurdities had been banished and reason alone was cultivated: the world could only be his pupil, not his enemy.

One striking contrast with Descartes is that, throughout so long a life, he had neither passion nor weakness. He never approached a woman: this was confirmed to me by the physician and the surgeon in whose arms he died. One may admire Newton for this, but one should not blame Descartes.

Public opinion in England about these two philosophers holds that the first was a dreamer, the other a wise man.

Very few people in London read Descartes, whose works have indeed become useless; very few read Newton either, because one must be very learned to understand him. Yet everyone talks about them; the Frenchman is given no credit, and the Englishman gets it all. Some people believe that if we no longer cling to the horror of a vacuum, if we know that air has weight, if we use telescopes, we owe it to Newton. Here he is the Hercules of fable, to whom the ignorant attributed all the deeds of other heroes.

In a London critique of Mr. de Fontenelle's speech, someone dared assert that Descartes was not a great geometer. Those who speak thus can reproach themselves for striking the nurse who raised them. Descartes made as great a journey from the point at which he found geometry to the point to which he advanced it as Newton made after him: he was the first to teach how to give algebraic equations for curves. Thanks to him, his geometry, now commonplace, was so profound in his day that no professor dared undertake to explain it, and hardly anyone in Holland except Schooten, or in France except Fermat, understood it.

He brought this geometric and inventive spirit to optics, which became an entirely new art in his hands; and if he made many mistakes in it, that is because a man who discovers new lands cannot at once know all their properties. Those who follow him at least owe him the discovery. I will not deny that all Mr. Descartes' other works swarm with errors.

Geometry was a guide he had, in a sense, fashioned for himself, and one that would surely have led him through physics; yet in the end he abandoned this guide and surrendered to the passion for systems. His philosophy then became nothing but an ingenious romance, plausible at best to the ignorant philosophers of his time. He was mistaken about the nature of the soul, the laws of motion, and the nature of light. He admitted innate ideas, invented new elements, created a world, fashioned man after his own pattern; and it is rightly said that Descartes' man is in fact Descartes' alone, far removed from the real man. He carried his metaphysical errors so far as to claim that two and two make four only because God willed it so; but it is not saying too much that he was admirable even in his wanderings. He was mistaken, but at least he erred methodically, following one consequence to the next. If he invented new fantasies in physics, at least he destroyed old ones: he taught the men of his time to reason and to use his own weapons against him. If he did not pay in good coin, it is no small thing to have discredited the counterfeit.

I do not believe anyone would truly dare compare his philosophy with Newton's in any respect: the first is an attempt, the second a masterpiece; but the man who set us on the road to truth may be worth as much as the man who later reached the end of that road.

Descartes gave sight to the blind; they saw the errors of antiquity and his own. The road he opened has since grown immense. Rohault's little book for a time constituted a complete physics; today all the collections of Europe's academies do not even make the beginning of a system: as this abyss was explored more deeply, it proved infinite. We must now see what Mr. Newton has excavated in this chasm.

On Descartes and Newton

A Frenchman arriving in London finds that philosophy, like everything else, has changed completely. He left a world full of matter and finds an empty one. In Paris, people see the universe as made up of whirlpools of subtle matter. In London, they see nothing of the kind. Back home, the Moon's pressure causes the ocean tides. For the English, the sea is drawn toward the Moon. So when you think the Moon ought to give us high tide, these gentlemen think it should be low tide. Unfortunately, there is no way to check this. To settle the matter, we would have had to examine the Moon and the tides at the very first moment of creation.

You will also notice that the Sun, which plays no part in this business in France, accounts for about a quarter of it here. For our Cartesians, everything happens through a push whose workings they scarcely understand. For Mr. Newton, it happens through attraction, whose cause they understand no better. In Paris, you picture the Earth shaped like a melon. In London, it is flattened on both sides. For a Cartesian, light exists in the air. For a Newtonian, it reaches us from the Sun in six and a half minutes. Your chemistry does everything with acids, alkalis, and subtle matter. Attraction rules even English chemistry.

The very nature of things has changed completely. You disagree about the definition of both the soul and matter. Descartes says that the soul is the same thing as thought, and Locke gives him quite a good argument to the contrary. Descartes also says that extension alone makes up matter. Newton adds solidity.

These are serious disagreements.

It is not my place to settle such great disputes between you.

The famous Newton, who brought down the Cartesian system, died in March of the year 1727. His fellow citizens honored him throughout his life, and he was buried like a king who had done good for his people. Here people eagerly read and translated into English Mr. de Fontenelle's Eulogy of Mr. Newton, delivered at the Academy of Sciences. People in England awaited Fontenelle's verdict as though it would formally declare English philosophy superior. But when they found that he had not only misunderstood that philosophy in describing it, but had also compared Descartes with Newton, the whole Royal Society of London rose in protest. Far from accepting his verdict, they sharply criticized the speech. Some people—and these were not the most philosophical—were offended by the comparison simply because Descartes was French.

We must admit that these two great men were very different in their conduct, their fortunes, and their philosophies.

Descartes was born with a vivid, powerful imagination. It made him an unusual man in both his private life and his way of reasoning. Even in his philosophical works he could not hide it: clever, striking comparisons appear at every turn. Nature had almost made him a poet. In fact, he wrote a verse entertainment for the queen of Sweden, which, for the sake of his reputation, has not been printed.

For a while he tried being a soldier. Later, when he had become a philosopher through and through, he did not consider love beneath him. He had a daughter named Francine with his lover. She died young, and he mourned her deeply. So he experienced everything that comes with being human.

For a long time he believed that he had to get away from people, and especially from his homeland, if he wanted the freedom to do philosophy. He was right. The people of his day did not know enough to teach him anything and were capable of little besides harming him.

He left France because he was looking for truth, which was being persecuted there by the wretched philosophy of the schools. But he found no more reason in the Dutch universities where he took refuge. In France, people were condemning the only claims in his philosophy that were true. Meanwhile, he was also persecuted by the so-called philosophers of Holland. They understood him no better, and because his fame was closer to them, they hated him all the more. He had to leave Utrecht. He faced an accusation of atheism, the slanderer's last resort. This man, who had used all his mental skill to seek new proofs that God exists, was suspected of not believing in God.

So much persecution suggested great talent and a brilliant reputation, and he had both. A little reason even broke through into the world despite the darkness of scholastic teaching and the prejudices of popular superstition. In the end his name became so famous that people tried to lure him back to France with rewards. They offered him a pension of a thousand écus. He came in the hope of receiving it, paid the costs of the official document, which was sold at the time, received no pension, and went back to pursue philosophy alone in northern Holland. Meanwhile, the great Galileo, at the age of eighty, was suffering in the prisons of the Inquisition for having proved that the Earth moves.

At last Descartes died early in Stockholm, partly because of an unhealthy routine. He was among a few scholars who were his enemies and in the care of a doctor who hated him.

Sir Newton's career was entirely different. He lived for nearly eighty-five years, always peaceful, happy, and respected in his own country. His great good luck was not only that he was born in a free country. He also lived at a time when scholastic nonsense had been cast out and reason alone was cultivated. The world could only become his pupil, not his enemy.

One striking difference between him and Descartes is that in such a long life he had no passions and no weaknesses. He never had relations with a woman. The doctor and surgeon in whose arms he died confirmed this to me. We may admire Newton for this, but we should not blame Descartes.

Public opinion in England holds that, of these two philosophers, the first was a dreamer and the second a wise man.

Very few people in London read Descartes, whose works have indeed become useless. Very few read Newton either, because understanding him takes a great deal of learning. Yet everyone talks about them. They give the Frenchman no credit and the Englishman all of it. Some people think it is thanks to Newton that we no longer cling to the horror of a vacuum, know that air has weight, and use telescopes. Here he is like the mythical Hercules, to whom ignorant people attributed all the deeds of the other heroes.

In a London critique of Mr. de Fontenelle's speech, someone dared claim that Descartes was not a great geometer. People who say that should feel ashamed of attacking the man who taught them. Descartes advanced geometry as far from where he found it as Newton advanced it afterward. He was the first to teach how to express curves as algebraic equations. Thanks to Descartes, his geometry has become commonplace today. In his day it was so difficult that no professor dared undertake to explain it. Hardly anyone understood it except Schooten in Holland and Fermat in France.

He brought the same talent for geometry and invention to optics, which became a completely new art in his hands. If he made many mistakes in it, that is because a man who discovers new lands cannot immediately know all their properties. Those who follow him at least owe him credit for the discovery. I will not deny that all Mr. Descartes' other works are full of errors.

Geometry was a guide he had in a sense made for himself, and it would have led him safely through physics. But in the end he abandoned that guide and gave himself over to system-building. From that point on, his philosophy was only a clever story, barely plausible even to the ill-informed philosophers of his day. He was wrong about the nature of the soul, the laws of motion, and the nature of light. He accepted innate ideas, invented new elements, created a world, and fashioned a human being to suit himself. People rightly say that Descartes' human being is really his alone, far removed from any real person. He took his metaphysical errors so far as to claim that two and two make four only because God wanted it that way. Still, it is no exaggeration to say that he deserved respect even when he went astray. He was wrong, but at least he was wrong methodically, moving from one conclusion to the next. If he invented new fantasies in physics, at least he destroyed old ones. He taught the people of his day to reason and to turn his own weapons against him. If he did not pay in good coin, it was still a great deal to discredit counterfeit coin.

To tell the truth, I do not think anyone would dare compare his philosophy with Newton's in any respect. The first is an attempt; the second is a masterpiece. But the man who set us on the road to truth may be worth as much as the man who later reached the end of that road.

Descartes gave sight to the blind. They saw the mistakes of antiquity and his own mistakes. The road he opened has since become vast. Rohault's little book served for a while as a complete system of physics. Today, even all the publications of Europe's academies together do not amount to the beginning of a system. As people explored this abyss more deeply, it proved infinite. Now we must see what Mr. Newton has uncovered in its depths.