On the representation of his colleagues his pension was restored so that he might have leisure to pursue his Remarques sur la langue française (1647).
In this work he maintained that words and expressions were to be judged by the current usage of the best society, of which, as a regular of the HĂ´tel de Rambouillet, Vaugelas was a competent judge.
He shares with François de Malherbe the credit of having purified French diction.
His book fixed the current usage, and the classical writers of the 17th century regulated their practice by it.Protests against the academical doctrine were not lacking.
He died in Paris in February 1650.His translation from Quintus Curtius, La Vie d'Alexandre (posthumously published in 1653), deserves notice as an application of the author's own rules.