Stephen Krashen

Stephen Krashen is an American linguist and professor emeritus at the University of Southern California known for his influential theories of second-language acquisition. His input hypothesis proposes that language learners acquire new language most effectively through comprehensible input, language slightly beyond their current level that they can still understand from context, rather than through explicit grammar instruction alone. Krashen's broader monitor model, which also includes the affective filter hypothesis describing how anxiety and motivation affect learning, shaped decades of second-language teaching methods and remains widely cited and debated in applied linguistics and language education research.