INFERENCE METHOD

In a production system having a memory for storing a group of rules each comprising a condition part and a conclusion part, inference means for inferring by using the group of rules and a working memory, whether a condition part is true or false in the working memory is determined, and if it cannot be determined, a rule having a conclusion part as to whether the fact is true or false is searched, and the conclusion part of the searched rule is used for backward reasoning. If the rule is not found by the search, an inquiry is made to a user.