Comprehensible output, from occurrence to acquisition: An agenda for acquisitional research

After over a decade of research into Swain's (1985) comprehensible output (CO) hypothesis, there is still a severe lack of data showing that learner output or output modifications have any effect on second-language (L2) learning. Izumi and Bigelow (2000, p. 245) argued that this is because, in most cases, researchers assumed rather than showed whether and how output helps with language learning. In this article, I will argue that this, in turn, is because existing research on CO was mostly descriptive in nature, focusing primarily on occurrence per se rather than acquisition or whether and how output can be a source of competence in the L2. I will outline a research agenda that makes acquisitional research central to the study of CO.