This paper explores the divergent forays made by Denis Diderot into aesthetic philosophy, focusing on the Art and Beau articles from the Encyclopédie, and the dialogue Rameau’s Nephew. Two central currents are identified running through this work, one emphasising rationality and the other questioning the limits of that rationality. Particular attention is paid to the influence the work of Francis Bacon had over Diderot and the tensions that result from that influence. The category of ‘genius’ is identified as the core of these tensions and Diderot’s disparate accounts of genius are shown to reveal the complexity and reflexivity of his thought. In this way, the aesthetic philosophy of Diderot indicates the internally inconsistent nature of much of his philosophy. At the same time it suggests that such inconsistency endows his work with a greater interest, pointing to and criticising certain vulnerabilities of enlightenment thought more generally.