Method and apparatus of parallel processing of multiple inference rules organized in fuzzy sets or logical functions of multiple fuzzy sets including membership functions defined in a so-called universe of discourse. The inference rules are configured essentially as IF-THEN rules with at least one antecedent preposition and at least one consequent implication. The prepositions have at least one term of comparison between membership functions and a plurality of input data and each term is separated by logical operators. The method associates with the logical operators maximum and minimum operations among two or more elements and calculates exhaustively the overall degree of truth (.OMEGA.) of a rule with a maximum or minimum of N partial truth levels. The method is accomplished by a plurality of identical, parallel inferential processors. Each inferential processor determines a preposition or a partial truth level of a preposition.