We describe how participants in an interaction use completions of each others' talk to bind themselves to a collective formulation of a matter in hand. In a corpus of problem-oriented discussions among groups of two or three people, we find speakers using sequences of completable utterance — putative completion — ratification to put their formulations of a problem-solution on a joint footing (a participant status that adds ‘collective author’ to Levinson's catalogue of producer footings). We describe the use of the completion sequence, and show how there are variations in its ratification stage (including explicit acceptance, repeating and reshaping).