  Rousseau’s most important philosophical impact was on Immanuel Kant. A portrait of Rousseau was the only image on display in Kant’s house, and legend has it that the only time that Kant forgot to take his daily walk was when reading Emile. Instances of direct influence include Kant’s idea of the categorical imperative, the third formulation of which in the Groundwork of the Metaphysic of Morals (the so-called formula of the kingdom of ends) recalls Rousseau’s discussion of the general will in The Social Contract. Ironically, Kant’s detachment of the idea of universal legislation from its context in the particularity of single society reverses Rousseau’s own approach, since Rousseau had, in preparatory work for The Social Contract rejected the idea of a general will of the human race as that notion appeared in Diderot’s article “Natural Right” in the Encyclopédie. Rousseau’s influence can also be seen in Kant’s moral psychology, especially in work such as Religion Within the Limits of Reason Alone, in Kant’s own thinking about conjectural history, and in his writings on international justice which draw on Rousseau’s engagement with the work of the Abbé St. Pierre.