SLA research began as an interdisciplinary field, and because of this it is difficult to identify a precise starting date. However, two papers in particular are seen as instrumental to the development of the modern study of SLA: Pit Corder's 1967 essay The Significance of Learners' Errors, and Larry Selinker's 1972 article Interlanguage. The field saw a great deal of development in the following decades. By the year 2010, second-language acquisition was studied from a wide variety of disciplinary perspectives, and there was a proliferation of different theories. However, the main two approaches were linguistic theories based upon Noam Chomsky's universal grammar, and psychological theories such as skill acquisition theory and connectionism.
The term acquisition was originally used to emphasize the subconscious nature of the learning process,
[Krashen (1982) made a sharp distinction between learning and acquisition, using learning to refer to the conscious aspects of the language learning process andacquisition to refer to the subconscious aspects. This strict separation of learning and acquisition is widely regarded as an oversimplification by researchers today, but his hypotheses were very influential and the name has stuck.]
but in recent years learning and acquisition have become largely synonymous.
There has been much debate about exactly how language is learned, and many issues are still unresolved. There are many theories of second-language acquisition, but none are accepted as a complete explanation by all SLA researchers. Due to the interdisciplinary nature of the field of second-language acquisition, this is not expected to happen in the foreseeable future.