Spectrum of Language Descriptions

ELIZA and a general grammar represent two extremes of the language processing spectrum:

• ELIZA:
  Too restricted. A large application, PARRY -- an artificial paranoid -- was attempted, but failed to get good enough coverage even with 10,000 patterns.

• General English Grammar:
  Too ambiguous. Hundreds of interpretations of ordinary sentences.

There is a very useful middle ground: semantic grammar.