What counts as legitimately sublime and what as counterfeit? The question of policing boundaries is internal to the sublime, and particularly fraught insofar as it is defined as transgressing limits of various kinds. If music is included in the sublime – by no means a foregone conclusion in its history – then what sort of music? Must it be violent, shocking or dissonant, transgressing orderly harmony in some obvious way? This chapter examines the fraught status and remit of harmony in the literary-critical discourse of the sublime. When music and musical concepts appear within broader scholarship on the sublime, they are often aligned with dissonance and irresolvability, as part of a construction of modernity likewise aligned with the breaking of old orders and harmonies. The chapter complicates this view through a double study of the late Romantic author Thomas De Quincey and his favourite singer, the Italian contralto Josephine Grassini. It examines both the multifaceted work to which music and harmony are put in De Quincey’s Confessions (1821), and the complexity of Grassini’s performances beyond the limits of the text, including her vocal traits, gendering, roles and repertoire during the Napoleonic wars, leading to reconsideration of sublimity’s relationship to pathos alongside harmony.