Ambiguous concepts play an important role in the reasoning that appears in our mental activity. Many expert systems have been developed as models of such kind of activities recently, but most of them cannot deal with ambiguous expression directly. This leads to difficulty of the knowledgebase construction and the input of ambiguous facts.
So we propose the knowledge representation dealing with ambiguous concepts and top-down reasoning method using it. We're able to treat ambiguous knowledge directly and get a satisfactory conclusion from the fewest facts by this proposed method.
The efficiency of this method is demonstrated via an examble.