Research on English variable adverb placement is largely focused on written evidence, with only rare insights from the vernacular. Moreover, no research has investigated adverb placement in longitudinal spoken data, meaning that little is understood about more historical stages in the operation of this system or how they relate to contemporary patterns. Drawing on a large multistage corpus, we pursue the question of what more distal stages of spoken language reveal with respect to patterns of adverb placement in vernacular English. Multivariate regression reveals not only that linguistic constraints condition variation in parallel to what is reported elsewhere, but that social factors are implicated as well. We also uncover diachronic evidence that the overall frequency of pre-auxiliary adverbs decreased between the mid-nineteenth and twentieth centuries, with one notable exception. Specifically, for modal + HAVE constructions, the pre-auxiliary position has historically been a particularly favorable one, and this order has increased significantly over time. Exploration of a possible explanation leads us to suggest that the increase in pre-auxiliary adverbs in modal + HAVE constructions is linked to the decrease in pre-auxiliary adverbs elsewhere, deriving from a parallel increase of HAVE reduction in vernacular speech. The results thus suggest an interaction between apparently independent processes in the verbal syntax of English.