Automated R e a s o n i n g techniques applied to the p r o b l e m of natural language correctness allow the d e s i g n of flexible training aids for the t e a c h i n g of foreign languages. The approach involves important advantages for both the student and the teacher by d e t e c t i n g possible errors and pointing out their reasons. Explanations may be given on four d i s t i n c t levels, thus offering differently instructive error messages according to the needs of the student.
