Theory of second language acquisition

Since it was proposed in the 1980s, Stephen Krashen's theory of second language acquisition has become one of the most important and widely accepted theories regarding the acquisition of a second language.

It consists of five main hypotheses: the Acquisition-Learning hypothesis, the Monitor hypothesis, the Natural Order hypothesis, the Input hypothesis, and the Affective Filter hypothesis.

In developing his theory, Krashen acknowledges "those scholars whose work has stimulated my own thinking in the early stages of the research reported on here: John Upshur, Leonard Newmark, and S. Pit Corder all recognized the reality of language "acquisition" in the adult long before I did".