The slow movement of Symphony No. 64 in A major, ‘Tempora mutantur’, has long intrigued Haydn scholars on account of its absent cadences and enigmatic form. The Latin title of the symphony is thought to be derived from the epigram by John Owen, a near-contemporary of Shakespeare, and it was used by Elaine Sisman to support her hypothesis that the slow movement formed part of Haydn's incidental music for Shakespeare's Hamlet. The enigma can be explained through an analysis informed by concepts native to eighteenth-century music theory. The absent cadences create instances of ellipsis, a rhetorical figure described by Johann Adolph Scheibe and Johann Nikolaus Forkel, and the form plays with a familiar template codified by Heinrich Christoph Koch. This analysis leads to a different interpretation. Rather than suggesting the protagonist of Shakespeare's tragedy, the movement stages a fictive composer in an act of musical comedy not dissimilar to that in Symphony No. 60, ‘Il Distratto’. The title comes not from Owen but from a Latin adage that was incorporated by Owen into his epigram. This adage had been popular in Germany since the Reformation and was then applied by one eighteenth-century music theorist to describe changes of musical conventions.