Mathematical fuzzy logic; decision making; evaluative linguistic expressions; rule-based systems; fuzzy control.

A methodology for construction of models using genuine expressions of natural language, namely the so called evaluative linguistic expressions is presented. A sophisticated formal theory of their meaning provides us a tool with a great application potential. These expressions occur also in conditional clauses of natural language which are gathered into linguistic descriptions, for example, of complex control or decision strategy. When applying a special reasoning method ? perception-based logical deduction ? we obtain models which effectively utilize expert knowledge and can mimic the way how people behave in complex decision situations. Applications especially in control and decision-making are also mentioned.