Beaugrand was both a lawyer and a mathematician. Descartes had contempt for him, saying so in so many words (AT II 25, CSMK 89). Descartes’ condemnation was strong, even by his own standards, referring to Beaugrand's appeal to living authorities in mathematical matters as testifying to his impudence and effrontery no less than his ignorance, and to his book on “geostatics” as so impertinent, ridiculous, and detestable as to cause wonder that anyone should have read it (those who did so generally shared Descartes’ view, if not his language in expressing it) (AT III 188–89). Indeed, in reaction to a letter of his that Mersenne conveyed after his death, Descartes urged that no more be sent because he already had enough toilet paper, which was the only use for Beaugrand's correspondence (AT III 437).

It is not irrelevant to these hard words that Beaugrand had accused Descartes of borrowing from Vieta, whose work Beaugrand had edited, and Harriot in his Geometry, which he had occasion to examine as secretary to the chancelier when Mersenne on Descartes’ behalf submitted the Discourse on Method and accompanying “Essays” for the privilège to publish. Nor is it irrelevant that Beaugrand himself was soon accused of plagiarism. Accusations of this sort are multiply difficult to deal with, but perhaps the most relevant feature for contemporary readers of Descartes is the perception of them in the period. Pascal's account (unaltered in its basic features by Baillet's later version, which nonetheless differs in some respects) is that Beaugrand sent to Galileo unsigned copies of solutions to problems concerning the cycloid by Roberval, Fermat, and Descartes, and did so in such a way as to lead one to think that the solutions were his own. (The imbroglio, on this account, was extended when upon Galileo's death the material was passed to Torricelli.)

See also Baillet, Adrien; Discourse on Method; Fermat, Pierre de; Galilei, Galileo; Mersenne, Marin; Pascal, Blaise; Roberval, Gilles Personne de