Maintenance of dialect differences despite loss of communicative isolation points up the need to analyze the role of dialect-standard alternates in signalling social identity and in contributing to conversational inference. Such analysis should focus on conversational interaction and on the processes by which situated interpretations are arrived at and used as frames for interpreting what follows. An Afro-American sermon and a disputed speech by a Black political leader to a mixed audience are analyzed. Dialect alternants serve to signal switching between contrasting styles in both. In the sermon, the audience shares with the speaker a knowledge of the structure of the activity and of the rules for both styles. In the speech, the activity lacks a predictable structure, only the style can frame interpretation, and most of the audience do not share its rules. Conversational inference is shown to depend not only on grammar, lexical meanings and conversational principles, but also on constellations of speech variants, rhythm, and prosody. Such constellations may persist as symbols of shared cultural background. (Dialectology, conversational and discourse analysis; Afro-American speech styles; urban United States.)