Abstract: There are many epithets for the European Enlightenment: ‘Radical Enlightenment’, ‘Pragmatic Enlightenment’, ‘Democratic Enlightenment’ and so on. This paper argues for one more, namely, ‘Principled Enlightenment’. It shows just how central the notion of principles was to many of the leading thinkers of the eighteenth century, paying special attention to the views of Etienne Bonnot de Condillac and Jean Le Rond d’Alembert. Principles are at the heart of their respective philosophical projects. Not only are their writings against systems predicated on a particular theory about how the principles of the sciences are discovered, but, it is argued, both philosophes are committed to a form of Principle Minimalism, whereby the fewer principles a science has the more fertile those principles are. And both believe that they have actually discovered just such a fertile principle, Condillac in his study of the origins of knowledge and d’Alembert in rational mechanics. Together these views of Condillac and d’Alembert are illustrative of the fact that there was indeed a principled Enlightenment
