Mental states and mental actions in planning
Andrew R. Haas · 1982
An intelligent agent needs to plan for mental goals as well as physical goals. A mental state can be an end in itself (trying to find out John's phone number) or a prerequisite to a physical action (finding out John's phone number in order to call him). A formal theory of mental states and actions is a first step towards a program that can plan to achieve mental goals. This thesis describes such a theory and its use in planning. The theory is an attempt to formalize naive psychology--what common sense says about the mind. The common-sense ideas we try to formalize are roughly as follows. An intelligent agent has beliefs, which can be true or false. New beliefs can be formed by perception, by introspection, or by deduction from old beliefs. An agent must retrieve a belief from his memory before he can use it. When an agent attempts to achieve a goal, he tries to infer from his beliefs that he can achieve the goal by executing a plan P. If he finds such a P, he will execute it. If you know an agent's goal and his beliefs, you can predict his actions fairly well by trying to find a plan P such that the agent's beliefs entail that he can achieve his goal by executing P. The theory says that an agent's beliefs are sentences of an internal language. This language resembles first-order logic except that it includes quotation. This allows agents to have beliefs about their own beliefs. A series of axioms in this quoted logic formalizes the ideas above. These axioms are used to prove correctness of a number of plans that involve mental actions and that predict the behavior of other agents. A proof-checking program tests that the axioms really entail the desired theorems. Thus the thesis formalizes knowledge about the human mind that has never been presented rigorously before. It applies this knowledge to two planning problems: planning mental actions, and planning to deal with other agents.