This article draws on work at the interface of grammar and interaction to argue that the clause is a locus of interaction, in the sense that it is one of the most frequent grammatical formats which speakers orient to in projecting what actions are being done by others' utterances and in acting on these projections. Yet the way in which the clause affords grammatical projectability varies significantly from language to language. In fact, it depends on the nature of the clausal (...) grammatical formats which are available as resources in a language: in some languages these allow early projection in the turn unit, in others they do not. We focus here on these two languages and show that their variable grammatical projectability has repercussions on the way in which three interactional phenomena – next-turn onset, co-construction, and turn-unit extension – are realized in the respective speech communities. In each case the practices used are precisely the ones which the clausal grammatical formats in the given language promote. The evidence thus suggests that clauses are interactionally warranted, if variably built, formats for social action. (shrink)