and possibly the most distinguished and rigorous 17th-century thinker after Descartes. Arnauld was a Jansenist, and the turbulent controversies of the time led to his losing his doctorate and being forced into exile in Belgium in 1679. With Pierre Nicole he was the author of La Logique, ou l’art de penser (‘Logic, or the art of thinking’), otherwise known as the Port-Royal Logic. His other main philosophical work is the Traité des vraies et des fausses idées (trs. as On True and False Ideas, 1990), which is a sustained attack on Malebranche.

Arnauld particularly disliked Malebranche’s representationalism, and the view that ‘we see all things in God’. At times he seems to espouse a direct realism about perception, although the Cartesian mistrust of the senses may make his position seem closer to that of Berkeley, who also holds that we directly perceive what really exists. The dispute became acrimonious, with Malebranche dwelling on Arnauld’s heresies, and Arnauld getting Malebranche’s Treatise on Nature and Grace placed on the Index of prohibited books.