Unlike Chapter 4 that forefronted the role of human cognition in noticing, processing and learning L2 input, this chapter places the ‘learner’ at the heart of L2A. It focuses on three major hypotheses: Input, Interaction and Output. The chapter begins with Krashen’s Input Hypothesis that introduced comprehensible input (CI) as a technical term to the field. The subject matters covered in this section include: the nature of processes of L2 attainment, acquisition versus learning (the Monitor Model), the nature of input (Natural Order Hypothesis [NOH], CI and i+1), the nature of L2 processing and production (Silent Period) and the role of individual differences (Affective Filter Hypothesis). Next is a brief description of the role of CI in different processes of interactions and participatory actions (e.g. communicative strategies) with different L2 speakers (Interaction Hypothesis [IH]). The last section on the Output Hypothesis concentrates on the importance of CI in processes of L2 use and production (language).

Input Hypothesis

Krashen’s Input Hypothesis (Krashen, 1985, 1987) is one of the most influential, if not the most comprehensive, theories that have described L2A. This theory is built on the perspective of a broad range of factors and processes, including (1) the nature of attainment processes (acquisition versus learning); (2) the nature of input (natural order, CI or comprehension hypothesis, i+1); (3) the nature of processing and production (role of first language [L1], silent period, monitor model); and (4) and the role of learner variables (affective filter, infantization). It is important to note four main points about Krashen’s work to understand it better. First, he is among a rare number of scholars in the field who went beyond the narrow pedagogical implications of his theories and research and (co)developed an actual method of L2 teaching, the Natural Approach (Krashen & Terrel, 1983).