Petis Versus Descartes

Petit was not as slow to surrender to Descartes as Fermat.

• Petit made more of his objections against the optics of Descartes than of those of De Fermat.

But whether he was a little prejudiced in his own favor, or whether his objections were effectively better, he took advantage of the advantage he had over De Fermat by means of his experiments, which, agreeing wonderfully “with the doctrine of Mr. Descartes,” served not a little to disabuse him and to make him seek his friendship early on.

Descartes had told Father Mersenne towards the end of February of this year that he did not remember ever having seen this Petit he was talking to him about in his letter, and whose objections he had sent him.

But whoever he might be, he had asked this father not to discourage him, and not to take away his desire to continue to write against him, without even using any consideration.

In the following month of April, he wrote back to this father to ask him to invite Mr. Petit to send him as soon as possible the rest of what he had to object against his optics, or anything else, so as not to be obliged to take up the pen twice to answer him.

As long Petit kept his remarks confined within the limits of optics, he did nothing contrary to his profession nor anything unpleasant to Mr. Descartes, who made it a diversion to answer him in his hours of recreation after the meal.

Petit was pressed by Father Mersenne to send Descartes the rest of what he had promised against his optics.

Having nothing in effect on this subject, had gathered something of what he had heard said in the air on the part of the discourse on the method concerning the existence of God and the immortality of the soul, in order not to pass for a light and boastful man in his promises. Father Mersenne, while waiting for what he was incessantly promising on optics, sent his paper to Descartes, who wrote back to him in these terms in the month of May of the same year.

**“I have not at all approved of the writing of Sieur Petit, and I judge that he wanted to be part of the party, and to make objections without having however anything to object.

For he only threw himself into some bad commonplaces, borrowed for the most part from atheists: and he heaps them up without much judgment, stopping mainly at what I have written of God and of the soul, of which he seems not to have understood a single word.

What had led me to ask you to get his objections against my optics from him, is because I believed that he had none, and that I doubted if he would be capable of making any that had any color without showing his lack of sufficiency. “But what made him promise to do so, is that he was afraid that one would ask him why he had not chosen for the subject of his objections optics, where he says he has employed ten or eleven years of study, rather than a matter of morals or metaphysics which is not at all of his profession.” This matter being able to be understood only by very few people, although everyone gladly gets involved in judging it, the most ignorant are capable of saying many things about it which pass for plausible among those who do not examine them very closely. Whereas in optics he could not enter into the matter so little, that one would not very obviously recognize his capacity. He has already shown it only too much, when he wanted to maintain that spherical lenses would be as good as hyperbolic ones, on the ground that he imagined that it was not necessary that they have more than an inch or half an inch in diameter.”**

Three months passed without Mr. Petit hearing from Mr. Descartes. Impatience made him go to find Father Mersenne, to know when the answers he was waiting for to the objections he had sent him on the existence of God could come. Father Mersenne, who knew the disposition of Mr. Descartes in this regard, did not dare to declare it to Mr. Petit for fear of putting him in a bad mood. To give him some satisfaction he wrote about it to Mr. Descartes in the month of September, and he asked him to write him something that he could show to Mr. Petit in order not to anger him. Mr. Descartes wrote to this father on the first day of October, that he was not in the habit of flattering his adversaries; and that if Mr. Petit was angry at his silence, he would have a lot more reason to be angry at an answer that he would make him, because he would certainly not spare him in a matter where he gave so much hold on him. The reasons that Mr. Petit had brought in his writing to prove the existence of God had seemed to him “so playful, that he seemed to have wanted to mock God in writing them.”

It is true that there was one that he had borrowed from the book of Mr. Descartes, but he had taken away all its strength by the change of place and the alteration he had caused to it. He therefore told Father Mersenne that he could tell Mr. Petit that he was waiting for his “objections against his optics, so that if they were worth the trouble, he could answer both at the same time.” But that as for what he had written of God, he would be afraid that one would mock them to see them dispute with each other on this matter, given that they were neither one nor the other theologians by profession.

Mr. Petit, having better informed himself in the sequel, did not remain for a long time among the adversaries of Mr. Descartes. Not content with becoming his friend he became his partisan and his defender: and Mr. Descartes having learned that he was taking a liking to his metaphysics that he gave two years later, considered this good effect as a true conquest, and he could not help but say about him when Father Mersenne told him the news, “that there is more joy in heaven for a sinner who converts, than for a thousand righteous who persevere.”

The dispute that Mr. Descartes had with Mr. Morin, a royal professor of mathematics in Paris, gave him more exercise than that of Mr. Petit, but it tired him less than that of Mr. de Fermat. It began on the 22nd day of February of the year 1638 by objections that Mr. Morin made him on light.

They are found printed in the first volume of the letters of Mr. Descartes: and one can say that they deserved the most to be preserved for posterity of all those that have been formed against the new opinions. Also Mr. Descartes judged them worthy of consideration as soon as he had received them, and preferable to those of Mr. Petit for their solidity, and for the nature of their difficulty. He wrote more than once to Father Mersenne to have him testify on his behalf to Mr. Morin, that not only had he received his writing in a very good part; but that he was still indebted to him for his objections, as being very proper to make him seek the truth more closely; and that he would not fail to answer them as punctually, as civilly, and as soon as he could. Mr. Morin had marked to him that he would find it very good that his objections were printed. Mr. Descartes promised him to arrange for them to be with the answer he would make to them on the conditions he would wish. He even offered to send his answer in manuscript to Mr. Morin, so that he could change or cut out what he would judge appropriate “before it was printed.” This is what he did in the following month of July, after having gained time by the delay that he had been obliged to bring to this printing. Mr. Morin had finished his objections with protestations of friendship, of esteem and of veneration altogether extraordinary for Mr. Descartes, and with complaints on the misfortune where he saw himself by the practices of his envious people, wishing that fortune were more favorable to him than it was ordinarily to the common of scholars. Mr. Descartes to whom this language was hardly suitable, had more trouble to answer this conclusion than to all the rest. “I do not at all pretend,” he says to him on this subject, “to deserve the courtesies of which you use with regard to me at the end of your writing, and I would nevertheless have no grace in refuting them. That’s why I can only say that I pity with you the error of fortune, in that it does not recognize your merit enough. But for my particular, thank God, it has never yet done me either good or bad: and I do not even know for the future if I should rather desire its favors than fear them. For as it does not appear to me honest to borrow anything from anyone that one cannot return with interest, it seems to me that it would be a great burden for me to feel indebted to the public.”

Father Mersenne who seemed to have joined some of his difficulties with the objections of Mr. Morin found the answer to these difficulties in that which Mr. Descartes made to the objections of Mr. Morin. They appeared both so satisfied with it that Father Mersenne wrote back to him the first day of the following August in the name of the two in these terms. “You have so consoled and enriched us with the excellent answers that you have made to Mr. Morin and to me, that I assure you that instead of thirty-eight sols of postage that was put on the package, seeing what it contained, I would have willingly given thirty-eight écus. We have read the answer together: and Mr. Morin has found your style so beautiful, that I advise you never to change it. For your similes and your rarities satisfy more than all that the others produce… you have, for the rest, done a great blow in the answer to Mr. Morin by showing that you do not despise, or at least that you do not ignore the philosophy of “Aristotle.” This is what has contributed to increasing the esteem that Mr. Morin testifies to have for you. This is also what I always assure those who, deceived by the neatness and the ease of your style, that you know how to lower to make it intelligible to the vulgar, believe that you do not understand scholastic philosophy: but I make them know that you know it as well as the masters who teach it, and who appear the most inflated with their skill.”

Mr. Morin, fearing to lose something of his reputation, if he was content with what Father Mersenne had done by writing to Mr. Descartes to thank him simply in the name of the two, did not fail to then examine his answer in the thought of finding matter for a reply. He replied in effect from the 12th day of the same month: and we still have this second writing inserted in the first volume of the letters of Mr. Descartes, and followed by a new answer that Mr. Descartes made there from the month of September with a diligence that surprised him, but which made him know that he had consideration for him. Mr. Morin pretended not to be entirely satisfied with this second answer, and he took the opportunity to make him a new reply in the month of October, in order to procure for himself the honor of writing the last. Mr. Descartes, always very far from ambitious for such a false glory, finished recognizing by this mark the character of the mind of Mr. Morin. He did not want to refuse him the satisfaction that he wished from him, since it cost him so little. That is why he told Father Mersenne towards the middle of the month of November that he would no longer make an answer to Mr. Morin since he did not desire it. Besides, there was nothing in the last writing of Mr. Morin, which could give him occasion to answer anything useful; and this work had only served to make him note that they were still more distant in sentiment on light, on the movement of the earth, and on the disposition of the heavens, than they were at the beginning of their dispute.