Abstract: A useful object-oriented knowledge base system is provided, which comprises an ‘object-oriented knowledge base’, an inference mechanism, and an ideal dictionary, etc. Sentences used as a ‘rule’ and/or as a ‘fact’ in the ‘object-oriented knowledge base’ are described according to a simple English grammar. Hierarchical structure of nouns-system in an ‘ideal thesaurus’ is constructed, on the basis of special kind of ‘object-oriented-lexical-definition of nouns’ recorded in the ideal dictionary. Lexical meaning of a verb whose meaning is specific are derived from that of a verb whose meaning is general and universal, by using ‘dichotomy’ on the basis of C-language-like way of description of English sentences in the lexicon. The hierarchical structure of verbs-system in an ‘ideal classification table’ is constructed on the basis of them.