The methods he used to collect data for his study of the varieties of English spoken in New York City, published as "The Social Stratification of English in New York City" (1966), have been influential in social dialectology. In the late 1960s and early 1970s, his studies of the linguistic features of African American Vernacular English (AAVE) were also influential: he argued that AAVE should not be stigmatized as substandard, but respected as a variety of English with its own grammatical rules. He has also pursued research in referential indeterminacy, and is noted for his seminal studies of the way ordinary people structure narrative stories of their own lives. In addition, several of his classes are service-based, with students going to West Philadelphia to help tutor young children while simultaneously learning linguistics from different dialects such as AAVE.