Simon Foucher

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Simon Foucher was the son of a merchant, Nicolas Foucher, and Anne Richot. No information has survived about his childhood and education. As the first relevant fact, his biographer reports that he was early ordained as priest and soon made honorary canon of the Sainte Chapelle of Dijon. Determined to continue his studies, after two or three years he moved to Paris, where he took a bachelor’s degree at the Sorbonne’s theological faculty. He spent in Paris all the rest of his life, mostly absorbed in intense intellectual work, which according to his biographer caused his premature death in 1696. Personally acquainted with some of the most prominent minds of the day, he got more and more involved in philosophical and scientific debates by means of his publications, his vast correspondence, and his attendance at the Paris Academy and other intellectual circles. Foucher’s Parisian lifestyle has been described as a “laborious retirement” (Rabbe 1867, p. 4), for the limited tasks of his ministry (he was chaplain of some nuns) left him ample leisure to cultivate his beloved subjects: mathematics, physics, and philosophy – with a special consideration for the history of Academic Platonism, which he strenuously tried to revive.

Arrived in Paris, he rapidly integrated himself into the scholarly scene of the capital and was able to forge close links with the Cartesian community. Baillet (1691, II, p. 439) reports that as Descartes’s remains were returned to Paris, Jacques Rohault asked Foucher to deliver a funeral speech, but the veracity of this episode is doubtful. A more plausible attestation of Foucher’s Cartesian connections is that starting from 1667 or 1668 he seems to have regularly attended Rohault’s philosophical Wednesdays, although it is not clear whether he already acted as the spokesperson of Academic skepticism and anti-dogmatism.

Foucher did not confine knowledge to pure speculation but also cultivated applied science and invention. At the end of 1672, he published a description of some new models of hygrometers (Nouvelle façon d’hygromètres, s.l., 1672; later in Id., Traité des hygromètres, 1686, pp. 9-34), which seems to have aroused Leibniz’s interest (cf. A II, 1, p. 637). Foucher’s first philosophical work (Dissertation sur la recherche de la vérité ou sur la philosophie des académiciens, où l’on réfute les préjugés des dogmatistes, tant anciens que nouveaux, avec un examen particulier des sentiments de M. Descartes) came out the following year in few copies, none of which has survived. In several letters to Leibniz, Foucher regrets being unable to send him a copy of this book, which he describes as “la Logique des Academiciens” (A II, 1, pp. 863-864; A II, 2, p. 196).

1675 was the turning year. As the first volume of Malebranche’s Recherche de la vérité appeared, Foucher anonymously published his Critique de la Recherche de la vérité, où l’on examine en même temps une partie des principes de M. Descartes (Paris 1675), where he renewed his attack against Cartesianism in the name of Academicism. This work gained him sudden exposure but also entangled him in sharp controversies with both Malebranche and the radical Cartesian Robert Desgabets, author of a Critique de la Critique de la Recherche de la vérité (Paris 1675). Foucher replied right away to the former with a Réponse pour la Critique à la Préface du second volume de la Recherche de la vérité (Paris 1676), but waited until 1679 and 1687 to publish, respectively, the first and the second part of his reply to the latter (Nouvelle Dissertation sur la Recherche de la Verité, contenant la Reponse à la Critique de la Critique de la Recherche de la Verité, etc., predated to 23 May 1676; Dissertation sur la Recherche de la Vérité, contenant l’Apologie des Académiciens, etc., Paris 1687).

Despite the open hostility of Malebranche’s initial reaction, Foucher did his best for avoiding an escalation. He refrained from intervening in Arnauld’s 1683 attack against Malebranche’s theory of ideas (cf. A II, 1, p. 863) and must have eventually succeeded in reconciling with the latter, as philosophical conversations with him are mentioned to Leibniz in 1685 and 1695 (cf. A II, 1, p. 879; A II, 3, p. 39). 

Foucher further authored works of poetry, moral philosophy (De la sagesse des anciens, 1682; Lettre sur la morale de Confucius, 1688), classical philology (his debate with Lantin on Carneades appeared in the Journal des Savants in 1691-1692), etc. For a list of his works see Papillon 1742.

Simon Foucher and Leibniz

Foucher and Leibniz became acquainted during Leibniz’s stay in Paris (1672-1676), certainly before April 1675 (cf. A II, 1, p. 386), and used to meet along with Mariotte at the experimental cabinet “dans la maison de M. Dalancé” (A II, 1, p. 203; presumably Joachim d’Alencé, astronomer and physicist). Leibniz also left a witty anecdote about his chance encounter with Foucher at a bookshop in 1675 (cf. A VI, 4, p. 2715).

After Leibniz’s Parisian stay, the two never met again. As Leibniz was still in Paris, however, a correspondence began as a sequel of their conversations and lasted almost until Foucher’s death. Leibniz first wrote in 1675, Foucher replied in 1678, and two further letters were exchanged in 1678-1679. In 1684, struck by Mariotte’s death, Foucher resumed the correspondence, which then continued mostly regularly until August 1693. The last exchange, consisting of three letters, took place between April and July 1695. A sequel of the debate, consisting of Foucher’s objections to the New System and Leibniz’s reply, was directly inserted in the Journal des Savants and is thus not strictly part of the correspondence (see above; cf. Leibniz to Nicaise, 24 September/4 October 1695, A II, 3, p. 92).

The most long-lasting object of discussion between Leibniz and Foucher is a cluster of epistemological and metaphysical topics revolving around skepticism: issues such as the knowability of truth, its provability, and the reliability of sense perceptions are debated from 1675 throughout the 168s and early 1690s. Leibniz later recounts that the existence of the external world had been also the subject of his Parisian live conversations with Foucher (A VI, 6, p. 374). As a modern proponent of academic skepticism, Foucher was alien to any form of hyperbolic doubt, and could thus appear to Leibniz as an ally against both Cartesianism and radical skepticism or Pyrrhonism. Far from blaming Foucher’s moderately skeptical penchant, Leibniz assimilates Foucher’s critical attitude towards unproved propositions to his own conviction that all assumptions should be demonstrated – even geometrical axioms and generally all truths of reason except identities. Contrary to Foucher, however, Leibniz rejects strict foundationalism: in order to progress, science is allowed to follow the “method of the geometers”, who provisionally assume a convenient set of unproved principles from which they derive conditional conclusions.

The two philosophers partially agree with each other also on truths of fact and the existence of the external world. Both maintain that some truths of fact, such as immediate perceptions, cannot be doubted. In 1675, Leibniz claims that the variety of our perceptions points to an external cause as it cannot be produced by the mind itself, but he agrees with the Skeptics that this allows no inference to the existence of material bodies. As for the regular connection of phenomena, it provides only moral and not absolute certainty.

In the subsequent correspondence, skeptical issues are discussed in relation to Foucher’s ongoing polemics. Malebranche’s 1678 skeptical turn on the existence of bodies and the nature of the soul is reported by Foucher as a victory of his own criticism. With Desgabets, on the other hand, no agreement was possible. In the great letter of 1686, Leibniz comments extensively on Foucher’s Réponse to Desgabets and takes cues from this debate to illustrate some of his typical doctrines, such as his famous characterization of the expression relation. As Foucher claims that ideas in the mind cannot represent the things outside if they do not resemble them, Leibniz points out that in order for one thing to represent another it is sufficient that the former expresses the letter, even without being similar to it. Thus, Leibniz introduces his theory of expression to neutralize the skeptical argument from dissimilarity. As for the question of whether extension is real or a mere phenomenon, Leibniz admits that the concept of extension is far from clear, but claims to be able to provide the analysis required to settle the issue.

In subsequent letters, the discussion on extension merges with a debate on physics and dynamics, occasioned by Leibniz’s controversy with the Abbé Catelan and Malebranche on the laws of motion and the Cartesian conservation principle. Both Foucher and Leibniz reject Descartes’s pysical laws as contrary to experience, but their surface agreement hides, in fact, opposite reasons. Contrary to Leibniz, Foucher considers the communication of motion as ultimately unintelligible; thus, he is not much impressed by Leibniz’s attempt to reformulate the conservation principle and use the concept of force to bridge the gap between physics and metaphysics. Moreover, he sees the principle that nature does not make leaps as leading back to the ancient paradoxes of motion. Leibniz replies that the skeptical objections would be sound only if the continuum were made up of indivisibiles, and that the failure of Descartes’s laws ruins the received view that body is mere extension.

The metaphysics of substance is another prominent subject in the correspondence. In 1686, commenting on the Foucher-Malebranche-Desgabets debate on pure intellect and brain traces, Leibniz revealed to Foucher his theory on the action and interaction of substances, and rejected both real influence and occasional causation. In 1687, he completed the picture with his views on animals and animated machines (A II, 2, p. 201). Along with Arnauld, Foucher was thus the first to learn about the hypothesis of concomitance and provide some (cautious) feedback (A II, 2, p. 290-291). Moreover, after the publication of the New System, he was absolutely the first to publicly discuss it, by raising objections that inaugurated the long term polemics on pre-established harmony (cf. Bilfinger 1723, §§ 122-134).

Further evidence confirm that in the 1680s and 1690s Foucher played an important role in the French reception of Leibniz’s name and thought. Starting from 1687, he made strenuous diplomatic efforts to secure Leibniz’s admission to the Académie des Sciences. However, the new membership was delayed, partly also because of Leibniz’s distrustful reluctance to apply; thus, Foucher did not live long enough to see his project realized. More successful was Foucher’s dissemination of Leibniz’s ideas. He circulated the manuscripts of part of their correspondence, published some letters in the Journal des Savants (1692-1693), and managed to insert in the same journal some resounding Leibnizian pieces, such as Extrait d’une lettre de Mr. de Leibniz, sur la question, si l’essence du corps consiste dans l’etendue (16 June 1691, pp. 259-262); De la chainette, ou solution d’un problème fameux proposé par Galiléi, pour servir d’essai d’une nouvelle analise des infinis etc. (31 March 1692, pp. 147-153); and the Système nouveau de la nature et de la communication des substances (27 June and 4 July 1695, pp. 294-306), followed by Foucher’s reply (Réponse de M. S. F. à M. de L. B. Z. sur son nouveau sistème de la communication des substances, 12 September 1695, pp. 422-426) and Leibniz’s clarifications (Eclaircissement du nouveau Système de la communication des substances, pour servir de reponse à ce qui a esté dit dans le Journal du 12. Septembre 1695, 2 and 9 April 1696, pp. 166-171).


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