How did PARRY's construction fundamentally contrast with ELIZA's operation?

PARRY attempted to embody a complex psychological model, while ELIZA used scripted patterns.

The core difference between ELIZA and PARRY lies in their underlying architectural ambition. ELIZA operated using relatively simple, observable methods: pattern matching and substitution, relying on scripted responses to mimic therapy. PARRY, conversely, was engineered to simulate a specific, complex internal state—paranoid schizophrenia. This meant PARRY attempted to embody a rudimentary psychological model that dictated its responses based on an assumed internal state of defensiveness and suspicion, making it more active and less purely reactive than ELIZA. While both systems relied on fixed rules, PARRY’s rules were organized to represent an internal belief system, whereas ELIZA’s rules were purely designed for conversational reflection.