柯拉申（Krashen）主張：學習（learning）不能轉化為習得（acquisition）。 在其 < 自然教學法 > （ The Natural Approach ）一書中，提出不少的教學活動，著重於 給予學生充分的語言資料輸入（ comprehensible input ），以確保語言的習得。柯氏似乎 特別強調自然溝通經驗在語言學習中的角色，而偏廢了文法教學的重要性。就語言習得理論 而言，他的觀點雖不難理解，卻也引來了不少批評的聲浪。究竟他的習得與學習說為何？何 以招致各方的批評？其他學者的看法如何？我們應如何看待其理論？本文將逐一闡述之。
Krashen claims that learning can not become acquisition. In The Natural Approach he suggests a wide variety of classroom activities centering on providing sufficient comprehensible input in order to assure the students' acquisition of the target language. He seems to emphasize particularly the role of natural communication experience in second language learning and to marginalize explicit grammar teaching. Krashen's position, in the light of second language acquisition theory comprehensible as that may be, has received a great deal of criticism, especially the Acquisition-Learning Hypothesis which dichotomizes the second language learning process into two separately operating systems: the acquired system and learned system. What does the Acquisition-Learning Hypothesis deal with? Why does it raise so many controversial issues? How do other linguists or psychologists treat these issues? How should we view these issues? This paper attempts to answer these questions.
