4. A fuzzy rule acquisition method according to claim 2, further comprising the steps of: obtaining at least one of the errors and grades of said propositions based on said inference error by referring to at least one of combinations of IF parts of said fuzzy rule, combinations of THEN parts of said fuzzy rules, and both of the combinations of the IF parts and the THEN parts of said fuzzy rules; if it is determined that there is a missing rule, selecting IF parts based on at least one of the errors and grades of the propositions of said respective IF parts of said fuzzy rules; and coupling said selected IF parts to generate the IF part of said missing fuzzy rule.
2. A fuzzy rule acquisition method according to claim 1, further comprising: a step of determining that there is a missing fuzzy rule if said step (d) determines that there is no contradiction for all of said fuzzy rules.