Interlanguage is based on the theory that there is a "psychological structure latent in the brain" which is activated when one attempts to learn a second language. Larry Selinker proposed the theory of interlanguage in 1972, noting that in a given situation the utterances produced by the learner are different from those native speakers would produce had they attempted to convey the same meaning. This comparison reveals a separate linguistic system. This system can be observed when studying the utterances of the learners who attempt to produce a target language norm.
To study the psychological processes involved one should compare the interlanguage of the learner with two things:
Interlanguage yields new linguistic variety, as features from a group of speakers' L1 community may be integrated into a dialect of the speaker's L2 community. Interlanguage is in itself the basis for diversification of linguistic forms through an outside linguistic influence. Dialects formed by interlanguage are the product of a need to communicate between speakers with varying linguistic ability, and with increased interaction with a more standard dialect, are often marginalized or eliminated in favor of a standard dialect. In this way, interlanguage may be thought of as a temporary tool in language or dialect acquisition.
An interlanguage is also a language that is used by speakers of different languages in order to be able to mutually communicate. This can be a national language such as English, or an international auxiliary language such as Interlingua or Esperanto.