In Error Analysis and Interlanguage, Corder introduced the idea that the learning of a second or foreign language is developmental and can be studied by analysing the errors that learners make. These errors should be viewed as signs of positive language development rather than deficiencies. Corder's argument that learner language, later termed 'interlanguage' by Larry Selinker (1972), is a language in its own right is now generally accepted.[1]