# Marin Mersenne

For the primes named after Marin Mersenne, see Mersenne prime.

Marin Mersenne, Marin Mersennus, or le Père Mersenne (September 8, 1588 – September 1, 1648) was a French theologian, philosopher, mathematician, and music theorist. In philosophy, he is mainly remembered in his connection with Descartes, for whom he compiled a series of objections which were published as part of Descartes' seminal Meditations on First Philosophy. Yet, this task was merely one instance of his contribution to the spread of the Enlightenment—much of his life was devoted to assisting various thinkers, and putting them in contact with one another.

## Contents

Mersenne's philosophical contributions are relatively modest, but show a deep concern with how the place of the new natural philosophy should be understood. Perhaps his main concern was combating the spread of radical skepticism. In Mersenne's view, the mathemetics-based science of Galileo and Descartes allowed a basis for the description of the natural world which was resistent to skeptical doubts. If skepticism could be so reigned in on one front, then the attitude of general skepticism (and so skepticism extending to religous doctrine) would become untenable.

## Life

Marin Mersenne was born near Oizé, Maine (present day Sarthe) on September 8, 1588. It appears that his family was of quite modest means, and it is likely that Mersenne received external financial support during the course of his studies. He began his education at the Collège du Mans, and continued at the Jesuit College of La Flèche, where he was a schoolmate of René Descartes (their friendship began later). In 1609, he moved to Paris in order to study theology at the Sorbonne, and was ordained in 1613. Two years prior to that, Mersenne joined the Order of the Minims, eventually taking up residence in their convent in Paris. It appears that the Minims allowed Mersenne substantial freedom to pursue his academic interests, and the convent remained his primary residence for the rest of his life.

Outside of philosophy and theology, Mersenne's chief interests lay in mathematics and music theory. Today, he is known in mathematics in connection with a formula for a certain set of prime numbers: $2^p - 1$, where p is prime. Though Mersenne did not discover the formula, his work on determining which values of 'p' yielded a prime number led to the set of numbers being dubbed "Mersenne primes." In music theory, Mersenne worked on determining the mathematical relationships between the vibrating frequencies of different tones.

In 1648, Mersenne died in Paris from complications arising from a lung abscess. He left a voluminous collection of letters, and a significant mark on the shape of academic pursuits in Europe.

## Philosophy

Mersenne's mature philosophical thought centered around attacks on Pyrrhonist skepticism, which had regained popularity in the early-seventeenth century. While Mersenne agreed that human knowledge was inevitably limited, he worries that more radical forms of skepticism threatened to undermine faith and marginalize the new scientific developments.

Pyrrhonist skepticism typically proceeds by finding some reason for doubting a given set of beliefs, and concludes that these beliefs should be abandoned (that assent should be withheld). Mersenne sympathized with this approach insofar as it undermined many forms of mysticism and alchemy, yet many Pyrrhonists extended their attacks to natural philosophy. What allows for such an extension, Mersenne believed, was the Scholastic view that natural philosophy was concerned with discovering and explaining the inner essences of things. Such inner essences cannot, he held, be known to us with certainty, so any discipline which attempts to understand them will fall to Pyrrhonist attacks.

Mersenne's alternative view of natural philosophy (the first serious presentation of which was his La verité des sciences of 1625) came from his assumption that no real doubts could be raised concerning either mathematics or our access to how things appear. Given this assumption, he reasoned, the application of mathematics to the nature of appearances must likewise be immune from doubt, and so should be the starting point for natural philosophy. When this position was first formulated in the 1620s, Mersenne primarily had in mind geometrical optics and mathematical approaches to music. Later exposure to the works of Galileo and Descartes led to his including mechanics in this group as well.

While Mersenne held that such mathematical branches of natural science should be privileged, he was not dismissive of merely probable disciplines. Such disciplines were capable of uncovering much truth and of being of great value—they simply were of no use in combating the spread of skepticism.

## References

### Primary Sources

• Euclidis elementorum libri, etc. (Paris, 1626)
• Les Mécaniques de Galilée (Paris, 1634)
• Questions inouies ou recreations des savants (1634)
• Questions théologiques, physiques, etc. (1634)
• Nouvelles découvertes de Galilée (1639)
• Cogitata physico-mathematica (1644)
• Universae geometriae synopsis (1644)

### Secondary Sources

• Brown, Harcourt. 1934. Scientific Organizations in Seventeenth-Century France (1620-80). Baltimore: Williams and Wilkins.
• Coste, H. de. 1649. La vie du R. P. Marin Mersenne, théologien, philosophe et mathématicien, de l’ordre des Pères Minimes. Paris. Reprtinted in P.T. de Larroque. 1972. Les correspondants de Peiresc 2. Geneva: Slatkine, 436–97.
• Dear, Peter. 1988. Mersenne and the Learning of the Schools. Ithaca: Cornell University Press. ISBN 9780801418754
• Hine, W.L., and B. Vickers (ed.). 1984. "Marin Mersenne: Renaissance Naturalism and Renaissance Magic," in Occult and Scientific Mentalities in the Renaissance. Cambridge: Cambridge University Press
• Lenoble, R. 1942. Mersenne et la naissance du mechanisme. Paris: Vrin.