The present contribution investigates the motivations underlying a tendency for phonological phrases in English to start with upbeats, i.e., unstressed syllables. The empirical part consists of two case studies based on a corpus of Early Modern English prose, and focusing on the variable use of the preposition _of_ introducing nominal complements of _(un)worthy_ and objects of gerunds, respectively. The counts provide quantified evidence indicating that the upbeat phenomenon is not only a corollary of the need for a function word signaling the beginning of a new phrase, but also a rhythmically motivated preference that exerts an influence on the presence or absence of a grammatical marker in phrase onsets. The phonological requirement for an upbeat thus has consequences for the syntactic makeup of phrases. In light of such empirical facts, it is argued that models of grammar conceptualizing the syntax-phonology interface as a unidirectional mapping are not tenable.