Krashen promoted his theory from the late 1970s and enriched it in the early 1980s. His theory has made a contribution to the understanding of second language acquisition, which centers around five fundamental hypotheses:the Acquisition-Learning hypothesis, the Monitor hypothesis, the Natural Order hypothesis, the Input hypothesis and the Affective Filter hypothesis. The Input hypothesis plays a central role for him, as he suggests, it may be the most significant notion in SLA of current times as it endeavors to deal the essential question about how we acquire language (Krashen, 1985). So this article will primarily focus on critically evaluating the Input hypothesis.
