Stephen Krashen is a linguist, educational researcher, and activist who is Professor Emeritus at the University of Southern California. In the 1990s, as the state of California became increasingly hostile to bilingual education, Krashen was instrumental in advocating the merits of learning a second language. His Acquisition-Learning Hypothesis is the centerpiece of his academic work.

Krashen’s Acquisition-Learning hypothesis revolves around the concept of “comprehensible input,” a term which essentially means “messages that can be understood.” Comprehensible input is best received when the learner is hearing something that he or she wants or needs to know. Krashen differentiates language learning from language acquisition, emphasizing that while learning is a formalized process, such as that which occurs in a classroom, acquisition happens informally, when a person is relaxed. He identifies a “silent period” during language acquisition, a time during which the student listens but is not comfortable speaking.

The Acquisition-Learning hypothesis acknowledges that students learn faster as they are given more comprehensible input. Inversely, a lack of comprehensible input delays language acquisition. Total Immersion Language Teaching, for example, succeeds so well is because it provides lots of comprehensible input. When people are immersed in a culture in which they do not know the language, they have an intense need and desire to speak that language. Such students are not interested in grammar lessons from a book but, instead, want to hear “comprehensible input” about that culture that teaches them what they need to know to survive.

Krashen’s acquisition-learning theory has much in common with both the communicative approach to language study and Noam Chomsky’s theory of generative grammar. The idea of “comprehensible input” is simply another way of saying that students learn languages best when they are learning about things that interest them. This idea is the essence of the communicative approach. Krashen’s Natural Order Hypothesis says that we acquire the rules of grammar in a logical order. This is similar to generative grammar’s hypothesis that the basic foundations of human grammar are deeply embedded in the human brain.

Stephen Krashen has been criticized for not having sufficient empirical evidence to back up his theories. Gregg accused Krashen of using “ill-defined terms.” McLaughlin critiques Krashen’s theories as being weak and imprecise. However, Krashen has conducted extensive research to determine the validity of his theories, and his dedication to promoting bilingual education has had undeniable worth. His frequent media appearances have pushed bilingualism to the forefront of public awareness.

Krashen is regarded true linguistic theorist, with over 30 years of research and hundreds of published articles and multiple books. Stephen Krashen’s passionate work has left an indelible mark on the future of bilingual education in America.

Some of Dr. Stephen Krashen’s research is available for free at www.sdkrashen.com, benikomason.net, http://web.ntpu.edu.tw/~lwen/publications.html, www.IJFLT.com.