Beethoven imitated Mozart's String Quartet in A major K464 more openly than any other work by a fellow composer. Yet critics have never explained his fascination with the fifth ‘Haydn’ quartet. This article argues that Beethoven responded to a rare and unexplored transformation of sonata form in which the primary theme returns at its original pitch in the secondary area. This preserves the melody of the theme, but reinterprets its harmonic and schematic function. Mozart explored this device with unusual rigour in k464, recalling the primary theme at pitch in both outer movements. The two primary themes share a common chromatic line whose invariant return wittily probes late eighteenth-century tonal conventions.

Beethoven emulated Mozart's harmonic design in his own Quartet in A major, Op. 18 No. 5, and even intensified its more problematic features. He imitated k464 most literally in the finale of the ‘Kreutzer’ Sonata, which provided a model for similar harmonic experimentation in the Sonata in G major Op. 31 No. 1, the ‘Waldstein’ Sonata and the first ‘Razumovsky’ quartet. k464 suggests an important source for Beethoven's use of chromatic elements to problematize tonal and thematic function, a practice most evident in the ‘Eroica’ Symphony.

Daniel Leeson recently noted an intriguing thematic borrowing in the Act 1 trio of Le nozze di Figaro (No. 7, ‘Cosa sento!’). As Leeson demonstrated, Basilio’s theme, first introduced in bars 16–23, derives from Cherubino’s preceding aria, ‘Non so più cosa son, cosa faccio’. This veiled allusion echoes throughout the trio, most dramatically during the narrative in which the Count reveals the hidden page. The quotation of Cherubino’s theme, Leeson argued, supplies the stage director with precious information. It proves that Basilio has eavesdropped on the previous scene, and explains why Susanna reacts so sharply to his seemingly innocuous opening lines: ‘By singing a disguised version of Cherubino’s tune to Susanna, Basilio suggests a nasty perspective on what might have transpired in the previous scene. Any possible accusation against the Count has, by Basilio’s hidden musical threat, been redirected: the insinuation targets Cherubino as the recipient of Susanna’s favours.’

Rhetorical studies of Mozart have assumed a rationalist conception of language, ignoring the empiricist model that actually dominated the Enlightenment. The two models, comparable structurally to the stile antico and style galant, collide in Mozart's learned finales. A study of three finales, from the Mass in C minor, the Concerto in E♭, K.449, and Die Entführung aus dem Serail, shows how Mozart negotiated irreducible contradictions within Enlightenment thought by switching between the two models.