Written and spoken language are known to differ substantially (Biber, 1988; 1995; Biber, Johansson, Leech, Conrad, & Finegan, 1999). Standard written language is highly uniform and governed by prescription, whereas the vernacular is most revealing of structured heterogeneity (Weinreich, Labov, & Herzog, 1968). We focus on four English morphosyntactic variables that problematize assumptions about the nature of variation in the vernacular: the genitive, the comparative, the dative, and relative pronouns. Each is characterized in casual speech by functional divides that reflect discrete configurations of variant use. After detailing the patterning of these variables in speech, we explore a characteristic arguably shared by each: its historical pathway into the language, where analogy and prestige were powerful motivations for variant choice. We suggest that this combination of systemic and social factors contributed to the nature of these variables in the vernacular grammar. Furthermore, we advocate for greater scrutiny of written and spoken data and the outcomes of change from above and below within each register. The type of innovation and its trajectory may affect the nature of the emergent variable grammar.