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Quotations in Context: Fontenelle

Michael Molinsky (University of Maine at Farmington)


“Mathematicians are like lovers. . . . Grant a mathematician the least principle, and he will draw from it a consequence which you must also grant him, and from this consequence another.”

I think I first encountered the above quotation by the French author Bernard Le Bovier de Fontenelle in E. T. Bell’s Men of Mathematics about thirty years ago. The origin of the quotation is Fontenelle’s most famous work, Entretiens sur la pluralité des mondes (Conversations on the Plurality of Worlds), first published in 1686 [Fontenelle 1686]. The book was intended to explain selected topics in science and astronomy to a popular audience; Fontenelle explained in the preface to the book that this was why he chose to write in French rather than Latin. The work was organized around conversations between a philosopher and a marquise that take place over the course of six consecutive evenings.

Portrait of Bernard Fontenelle.
Painting of Fontenelle by Hyacinthe Rigaud, 1713. Public domain, Wikimedia Commons.

The subject quotation for this column is taken from the conversation on the fifth evening:

Ecoutez, Madame, répondis-je, puis que nous sommes en humeur de mêler toûjours des folies de galanterie à nos Discourse les plus serieux, les raisonnemens de Mathematique sont faits comme l’Amour. Vous ne sçauriez accorder si peu de chose à un Amant, que bien-tost aprés il ne faille luy en accorder davantage, & puis encore davantage, & à la fin cela va loin. De mesme accordez à un Mathematicien le moindre principe, il va vous en tirer une consequence, qu’il faudra que vous luy accordiez aussi, & de cette consequence encore une autre, & malgré vous-mesme il vous mene si loin, qu’à peine le pouvez vous croire. Ces deux sortes de Gens-là prennent toûjours plus qu’on ne leur donne [Fontenelle 1686, pp. 308–310].

Hear me, Madam, says I, since we are in the humour of mingling Amorous Follies with our most serious Discourse, I must tell you, that in Love and the Mathematicks, People reason alike: Allow never so little to a Lover, yet presently after you must grant him more; nay, more and more; which will at last go a great way. In like manner, grant but a Mathematician one little Principle, he immediately draws a Consequence from it, to which you must necessarily assent; and from this Consequence another, till he leads you so far (whether you will or no) that you have much ado to believe him. These two sorts of People, Lovers and Mathematicians, will always take more then [sic] you give ‘em [Fontenelle 1715, p. 140].

You might be surprised to learn that the context in which this quotation appears is a discussion of the likelihood of the existence of life on other planets. Here are the sentences that immediately follow the selection given above:

Vous convenez que quand deux choses sont semblables en tout ce qui me paroist, je les puis croire aussi semblables en ce qui ne me paroist point, s'il n'y a rien d'ailleurs qui m'en empesche. De là j'ay tiré que la Lune estoit habitée, parce qu'elle ressemble à la Terre, les autres Planetes, parce qu'elles ressemblent à la Lune. Je trouve que les Etoiles Fixes ressemblent à nostre Soleil, je leur attribuë tout ce qu'il a. Vous estes engagée trop avant pour pouvoir reculer, il faut franchir le pas de bonne grace [Fontenelle 1686, pp. 310–311].

You grant that when two things are like another in all visible respects, it is possible they may be like one another in those Respects that are not visible, if you have not some good reason to believe otherwise: Now this way of arguing have I made use of. The Moon, says I, is inhabited, because she is like the Earth; and the other Planets are inhabited, because they are like the Moon; I find the fix’d Stars to be like our Sun, therefore I attribute to them what is proper to that: You are now gone too far to be able to retreat, therefore you must go forward with a good Grace [Fontenelle 1715, pp. 140–141].


Fontenelle, Bernard de. 1686. Entretiens sur la pluralité des mondes. Paris: C. Blageart.

Fontenelle, Bernard de. 1715. Conversations on the Plurality of Worlds. Translated by William Gardiner. London: A. Bettesworth.

“Quotations in Context” is a regular column written by Michael Molinsky that has appeared in the CSHPM/SCHPM Bulletin of the Canadian Society for History and Philosophy of Mathematics since 2006 (this installment was first published in May 2015). In the modern world, quotations by mathematicians or about mathematics frequently appear in works written for a general audience, but often these quotations are provided without listing a primary source or providing any information about the surrounding context in which the quotation appeared. These columns provide interesting information on selected statements related to mathematics, but more importantly, the columns highlight the fact that students today can do the same legwork, using online databases of original sources to track down and examine quotations in their original context.


Michael Molinsky (University of Maine at Farmington), "Quotations in Context: Fontenelle," Convergence (February 2024)