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Onderwijs / Teaching | Publicaties / Publications | Research project: Descartes and his Network | Unknown letter Descartes discovered (2010)

An Unknown Letter of René Descartes

To Marin Mersenne, 27 May 1641

In the library of an American college a Utrecht scholar has found an unknown letter of the French philosopher René Descartes (1596−1650). The letter provides a unique insight into the history of one of Descartes' main works, the Meditationes de prima philosophia (1641) — a book which at the time he wrote the letter was being printed at Paris under the supervision of the friend to whom he addressed the letter, Marin Mersenne.

The Correspondence

The correspondence is an invaluable addition to our understanding of the life and works of Descartes. In his letters Descartes raises topics he does not touch upon in his published writings, or he explains, qualifies and elaborates claims made in the published works. The correspondence is also the place where to find Descartes' comments on the plans and achievements of his contemporaries. Furthermore, they supply us with a unique insight in his own plans, ambitions and disappointments. His most important correspondent was Marin Mersenne (1588−1648), virtually his only regular contact outside the Dutch Republic, with whom he discussed whatever occupied his mind, or Mersenne's. Approximately 800 letters of the correspondence are known one way or another, about 145 of which are addressed to Mersenne. We still have less than 200 autograph letters (the letter as actually sent). The most recent discoveries of autograph letters date from 2002 (two letters, in Studia Leibnitiana 34 (2003)), the last one before that was published in 1975. Mention should also be made of a letter to Cornelis van Hogelande on Comenius, published in 2004, even though that is a copy and not an autograph.

A Completely Unknown Letter

Descartes wrote the recently discovered letter on 27 May 1641 at Endegeest castle, close to Leiden. It is part of an intensive exchange between Descartes and Mersenne in view of the publication of the Meditations on Metaphysics, which, together with a series of Objections and Replies by other philosophers and theologians, would be published in Paris later that year, August 1641. The letter provides an answer to various questions concerning the way that work was printed. Moreover it throws an interesting light on certain key notions of Descartes' philosophy. Finally it shows that in its original form the Meditations was differently organized. This letter is remarkable, not only for its sensational contents, but also because no abstracts or summaries were known. The letter is published in Archiv für Geschichte der Philosophie, 92 (issue 3, 2010), 290–302.
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By means of the letter Descartes confirms having received the first four printed sheets (corresponding to 64 pages) of the Meditations. As a result we now know that printing started at the beginning of May 1641. As yet, Descartes has not read them accurately (the first sheet is missing moreover), being more interested in the Objections of the famous philosopher Pierre Gassendi (1592−1655), which Mersenne had sent by the same mail. In later correspondence Descartes has nothing but scorn for Gassendi's objections — in this letter he shows himself rather pleased: he likes the style and Gassendi's criticism provides an excellent opportunity to clarify his ideas. In view of this letter the question arises why Descartes reacts so hostily in letters of a later date.

The newly found letter also contains a discussion of texts Descartes had sent to Mersenne much earlier. Among other things he clarifies his idea of God as causa sui (cause of himself), an idea discussed in his replies to the First Objections written by the Alkmaar priest and learned theologian Johannes Caterus (c.1590−1655). Meanwhile the idea had been criticised by other theologians and philosophers, particularly Antoine Arnauld (1612−1694), author of the Fourth set of Objections. Descartes asks Mersenne to make specific corrections, none of which however were actually carried through. Further research should clarify the significance of these emendations and try to answer the question why they did not find their way to the final text of the Meditations.
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Revision of the Meditations

The most important historical information can be found at the end of the letter, where it emerges that originally the Meditations were conceived along different lines. Descartes asks Mersenne to completely eliminate three texts: a Latin translation of Pt 4 of the Discourse on method (originally published in 1637), a preface to the Meditations and a preface to the Objections and Replies. They should be replaced by a new general preface, which corresponds to the preface that was printed eventually. The reason for those changes is that a French visitor has convinced Descartes of the good intentions of Pierre Petit (1598−1677), who had been very critical of part 4 of the Discourse — criticism about which Descartes was extremely upset. Now that he knows that Petit changed his mind Descartes has no reason to react to him personally — in the new preface he limits himself to a few general remarks about the criticisms that reached him concerning the Discourse, without naming anybody.

According to Descartes' 17th century biographer Adrien Baillet, the French visitor would have been a certain Abbé de Touchelay, of whom we know very little. He lived at Tours, where Descartes visited him in 1644. He was a good friend of Claude Picot (1601−1668), in whose company he visited Descartes. Picot became a close friend of the French philosopher, and he translated Descartes' Principia philosophiae (1644) into French.
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Titlepage Meditationes de prima philosophiae (1641)


The letter consists of four densely written pages. Its authenticity is beyond any doubt, not only because of the signature and the handwriting (which are unmistakeably Descartes') but also because a letter to Mersenne of that date figures in two inventories of Descartes' correspondence that were made c.1690 and 1800. Originally they were part of the collection of the Institut de France, from which they were stolen, together with thousands of other letters and documents by Count Guglielmo Libri (1803−1869), professor of mathematics at the Collège de France and secretary of the Committee for the General Catalogue of Manuscripts in French public Libraries (Commission du Catalogue général des manuscrits des bibliothèques publiques de France ). Despite the fact that French libraries managed to retrieve a part of those collections, it is, on the basis of the lists made in 1690 and 1800, certain that some letters are still missing.
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Charles Roberts Collection

The letter is now being kept in the Charles Roberts Autograph Letter Collection at Haverford College (Haverford, PA, USA). Charles Roberts (1846−1902), a graduate of Haverford College in 1864, was inspired to begin what would become a magnificent collection of autograph letters after receiving a letter addressed to him personally by Abraham Lincoln. This letter (dated November 17, 1860) is now part of this valuable collection, ranging from a set of the Signers of the Declaration of Independence, letters of Presidents of the United States, foreign royalty, distinguished American and foreign authors and composers and scientists. After Roberts' death his widow, Lucy Branson Roberts (1856−1937), donated the collection to Haverford College in 1902. It is not known when Roberts obtained the letter of Descartes. Presumably the letter was put up for auction by Libri in the 1840s, after which it changed hands several times before it was acquired by the American collector. The president of Haverford College, Dr. Stephen Emerson, has taken contact with the Institut de France over restitution. This will be done June this year during a solemn session at the Institut de France.
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The Discovery

Dr. Erik-Jan Bos, research-fellow of Zeno-Institute, the research institute of the Department of philosophy of Utrecht University (the Netherlands), found a brief and undetailed mention of the letter in a description of the Charles Roberts Collection at Haverford College library. Thanks to the generous co-operation of Mr. John Anderies, Head of Special Collections at Haverford College, it became clear that it was an authentic unknown letter of Descartes. Mr. Anderies also supplied a paper written by a Haverford College student in 1979, which is entirely devoted to the letter. This paper by Mr. C. Turner is kept in the same file as the letter, providing an introduction as well as a transcription and English translation. He rightfully recognized that the letter was unknown. It went unpublished, and so Descartes scholars failed to learn of its existence.

Dr. Erik-Jan Bos works on a new critical edition of Descartes' complete correspondence, which will be published by Oxford University Press. His project is part of a larger project 'Descartes and his Network,' directed by Prof. Theo Verbeek, which is sponsored by NWO (the Netherlands Organisation for Scientific Research).
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What the Media say (selection)

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See the website of the Institut de France.

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