(eng): The paper returns to the problem of derivation of a conclusion on the basis of fuzzy IF-THEN rules, which are interpreted as genuine linguistic sentences consisting of evaluating linguistic expressions. Sets of fuzzy IF-THEN rules are called linguistic descriptions. Perceptions are linguistic expressions derived on the basis of observation in a concrete context. They can be used in logical deduction which gives a piecewise continuous function. The paper contains a method for making it smooth.