Uncertalnty and indetermlnacy are typlcal of expert knowledge in humanlties. Data processed by an expert (e. g. a medlcal doctor) are often imprecise, uncertaln, and indeterminate. It is, however, these data according to whlch the expert has to make his/her decisions. Processing of indeterminate and uncertain data Is the subject of fuzzy logic, whlch deals with fuzzy sets. In a broad variety of sltuations and tasks for whlch no precise mathematlcal models are avallable, an expert Is able to formulate his/her knowledge and problém solving stratégy In a natural language by meansof so-called"if-then"rules.Rule-based fuzzy systems, which are based on these rules, represent a mathematical model that results dlrectly from the experťs experience descrlbed In a natural language. In addltion to that, fuzzy systems provlde us with a means of communicatlon easlly usable and thus comprehensible by a computer. Fuzzy systems can be applled to a broad spectrum of sítuations in medicíně, such as diagnostic expert systems and feedback fuzzy control devlces.

        Key words: logic - indeterminacy - linguistic description - fuzzy control