FUZZY OBSERVER DESIGN In practical applications, the state of a system is often not readily available. Under such circumstances, the question arises whether it is possible to determine the state from the system response to some input over some period of time. For linear systems, a linear observer w1x provides an affirmative answer if the system is observable. Likewise, a systematic design method of fuzzy regulators and fuzzy observers plays an important role for fuzzy control systems.