There was no such thing as science in the French Enlightenment, and this is a chapter about it. There were, of course, sciences in Enlightenment France, many of them, and they were essential to the Enlightenment no matter how we define the term (as a historical period, a cultural or philosophical movement, a normative agenda, etc.). But since science in the portentous singular is a creation of the late nineteenth century, only by shearing the term ‘Enlightenment’ of many of its most important referents - not least its attachment to the eighteenth century - can we sustain the category ‘Enlightenment science’ as a singular, monolithic concept. The Encyclopédie edited by Denis Diderot and Jean-Baptiste le Rond d’Alembert illustrates the point, for, while this most scientific of Enlightenment tomes has an entry on ‘science’, the article defines the term traditionally as secure and reliable knowledge in any domain, not as some separate kind of extra-reliable knowing. Within this un-modern understanding, talk of a science of poetry or a science of painting could proceed without generating any dissonance, and apparent sciences such as engineering or medicine could be placed outside the sciences proper because of their reliance on artful craft. D’Alembert’s ‘Systéme figuré des connaissances humaines’ [’Figurative System of Human Knowledge’], which taxonomically opens the Encyclopédie, illustrates the modernizing changes afoot around 1750, since many of the fields we would call ‘science’ appear under his rubric of ‘Reason’, while poetry, painting and the literary arts are all grouped separately under the rubric of ‘Imagination’. This is the division we would expect. But a third category, ‘Memory’, challenges our sense of order by including both planetary science and the literary art of the memoir. ‘Reason’ also includes rhetoric, grammar and the other ‘arts of communication’, together with seemingly scientific fields such as mathematics. In short, any attempt to find our modern disciplinary divisions in d’Alembert’s tree, or in the Encyclopédie more generally, is doomed to frustration.