Early twentieth-century French critics often characterised Debussy’s music as ‘natural’. A seemingly banal descriptor of a radically novel musical language, the attribution of ‘naturalness’ drew from a broad range of ideas in the burgeoning human sciences of the time, from post-Helmholtzian acoustics and the physiology of hearing to theories of emotion in the emerging nouvelle psychologie. At the same time, the supposed ‘naturalness’ of Debussy’s music stood in tension with a recognition among some Debussyist critics that ‘natural’ music remained, at bottom, a contradiction in terms. Surveying accounts of music and naturalness in the writings of three critics active in Debussyist conversations – Paul Landormy, Lionel de la Laurencie, and Michel-Dmitri Calvocoressi – this essay explores both the intellectual borrowings and influences that informed their accounts of Debussy’s music and, more broadly, the ways in which these specific conversations contributed to changing ideas about the elusive category of ‘music’ itself.