Jean Le Rond d'Alembert

Lore & Background

Born in Paris, d'Alembert was the natural son of writer Claudine Guérin de Tencin and artillery officer Louis-Camus Destouches. Days after birth his mother left him on the steps of the Saint-Jean-le-Rond de Paris church; he was named after the patron saint. His father placed him with the wife of a glazier, Madame Rousseau, with whom he lived for nearly 50 years. Destouches secretly paid for his education but did not want his paternity officially recognised. He later scorned Cartesian principles taught by the Jansenists. He also was interested in medicine and mathematics, and changed his name from Jean-Baptiste Daremberg to d'Alembert. When the Encyclopédie was organised in the late 1740s, he was engaged as co-editor with Diderot, authoring over a thousand articles including the famous Preliminary Discourse.

Reader's Guide

D'Alembert's significance lies in his contributions across mathematics, physics, philosophy, and music theory. His wave equation and D'Alembert's formula are foundational in mathematical physics. In France, the fundamental theorem of algebra is named the d'Alembert–Gauss theorem, acknowledging his work though an error in his proof was later corrected by Gauss. He created the ratio test for series convergence. As co-editor of the Encyclopédie, he shaped Enlightenment thought, authoring over a thousand articles and the Preliminary Discourse. His philosophical stance, doubting whether anything exists outside us corresponding to what we suppose we see, aligned with Berkeley and anticipated Kant. In fluid mechanics, d'Alembert's paradox—that drag on a body in an inviscid, incompressible fluid is zero—remains a classic problem. His music theory work popularised Rameau's principles, though he misconstrued some details. D'Alembert's legacy includes the d'Alembert operator. He died of a urinary bladder illness and, as a known unbeliever, was buried in a common unmarked grave.

Did You Know?

• D'Alembert was the natural son of writer Claudine Guérin de Tencin and artillery officer Louis-Camus Destouches, and was left on the steps of a church days after birth.
• He lived with the wife of a glazier, Madame Rousseau, for nearly 50 years; she told him he would 'never be anything but a philosopher.'
• Frederick the Great proposed naming a suspected moon of Venus after d'Alembert, but d'Alembert refused the honor.
• D'Alembert's proof of the fundamental theorem of algebra contained an error later corrected by Carl Friedrich Gauss.