Speakers often construct their utterances based on the immediately co-present utterances of dialogue partners. They array their linguistic resources parallel to their partners’ and activate resonance. Based on the theories of dialogic syntax and cognitive linguistics, this study undertakes to explain how speakers activate resonance and how parallelism contributes to constructing linguistic forms as well as to shaping the ongoing flow of conversation. Three phases of resonance activation are illustrated in relation to cognitive processes: (a) parallelism constituted with extension of multiple categories in synthesis; (b) parallelism meeting or failing the previous speaker’s intention due to schematization; and (c) parallelism achieved as a consequence of priming through schematization and extension. It is concluded that linguistic forms develop in the ongoing flow of socially coordinated cognition, where patterns emerge through activation of mapping relations between linguistic elements. This process is anchored in speakers’ concepts of grammatical equivalences, ability of categorization, and grasp of linguistic conventions.