The document discusses the complex relationship between language input and intake in second language acquisition, highlighting a fundamental mismatch between what is taught and what is learned. It explores various theories including behaviorist, innatist, and interactionist frameworks, emphasizing how learner language, or interlanguage, develops through distinct processes influenced by both native language transfer and interaction with others. Additionally, it underscores the importance of both explicit and implicit knowledge in language teaching, suggesting that effective instruction must accommodate different types of language acquisition.