ABSTRACT: There are three major views of language acquisition. The Comprehension Hypothesis, the Comprehensible Output Hypothesis, and the Skill-Building Hypothesis. Only the Comprehension Hypothesis is fully consistent with all case histories of language acquirers, including cases of polyglots and those who have acquired language despite handicaps.
Krashen, S. 2014. Case Histories and the Comprehension Hypothesis. TESOL Journal (www.tesol-journal.com),
Available for free download: http://www.sdkrashen.com/articles.php?cat=6