Abstract: A natural language parser creates parsed commands or output for an external system from user commands entered on a user interface. The parser utilizes symbols arranged in an object-oriented hierarchical manner, and a grammar information and state table to constrain language inputs so that they conform to requirements of the external system. The parser provides feedback to the user via the user interface to assist in the formation of valid output to the external system and reduce the complexity for the user. The parser may be applied to the field of control systems in general, as well as a flight control system for an aircraft.