Abstract: In a grammar checking system which includes first tagging a sentence as to parts of speech, an improper determiner correction module detects improper referents of a noun phrase and suggests insertion of a determiner should one be necessary or the deletion of an improper determiner. To detect improper use of a determiner, parts of speech tags are utilized to characterize a sentence, thus to identify noun phrases by maximally matching a pattern that defines which sequences of parts of speech tags constitute valid noun phrases. This is accomplished by identifying the start of the noun phrase and its end to permit checking for either missing determiners, extraneous determiners, or lack of agreement in number for the constituents of the noun phrase.