This paper describes an approach to computer-assisted language instruction based on the application of artificial intelligence technology to grammatical error diagnosis. We have developed a prototype system, Scripsi, capable of recognising a wide range of errors in the writing of language learners. Scripsi not only detects ungrammaticality, but hypothesizes its cause and provides corrective information to the student. These diagnostic capabilities rely on the application of a model of the learner's linguistic knowledge.
Scripsi operates interactively, accepting the text of the student's composition and responding with diagnostic information about its grammatical structure. In contrast to the narrowly defined limits of interaction available with automated grammatical drills, the framework of interactive composition provides students with the opportunity to express themselves in the language being learned.
Although Scripsi's diagnostic functions are limited to purely structural aspects of written language, the way is left open for the incorporation of semantic processing. The design of Scripsi is intended to lay the groundwork for the creation of intelligent tutoring systems for second language instruction. The development of such expertise will remedy many of the deficiencies of existing technology by providing a basis for genuinely communicative instructional tools --- computerised tutors capable of interacting linguistically with the student.
The research is based on the assumption that the language produced by the language learner, ``learner language'', differs in systematic ways from that of the native speaker. In particular, the learner's errors can be attributed primarily to two causes: the operation of universal principles of language acquisition and the influence of the learner's native language. A central concern in the design of Scripsi has been the incorporation of a psychologically sound model of the linguistic competence of the second language learner.
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