Interlanguage Theory

Interlanguage theory is a theory of second language acquisition introduced by linguist Larry Selinker in a 1972 paper, describing the distinct, evolving linguistic system that a language learner constructs at any given point in their learning, a system with its own internally consistent rules that differs systematically from both the learner's native language and the target language they are learning. Selinker argued that a learner's errors are not simply random failures to master the target language's rules but evidence of a rule-governed interlanguage system shaped by processes such as transfer from the native language, overgeneralization of target-language rules, and simplification strategies, and that this interlanguage develops through a series of stages as the learner receives more input. The theory reframed how language teachers understand learner errors, treating them as a natural and informative part of a systematic developmental process rather than simple mistakes to be corrected away, and it remains a foundational reference point in second language acquisition research and language-teacher training.