In Paris, Condillac was involved with the circle of Denis Diderot, the philosopher who was co-contributor to the "Encyclopédie". He developed a friendship with Jean-Jacques Rousseau, which lasted in some measure to the end of his life. It likely started when Rousseau was a tutor to two of his brother Jean's sons in Lyon—Jean Bonnot de Mably was then provost of the police and known as Monsieur de Mably. Together with his brother Gabriel, who became the well-known political writer known as Abbé de Mably, Condillac introduced Rousseau to an intellectual circle.