A system for controlling a target apparatus includes a supplying section, a reasoning section, and a control section. The supplying section supplies n states of the target apparatus (n.gtoreq.2 and an integer). The reasoning section receives the n sensed states as n results from the supplying section and performs fuzzy backward reasoning for data representing the n results and causality data to generate certainties of m causes (m.gtoreq.2 and an integer). The control section controls the target apparatus in accordance with the certainties of the causes.