Using Descriptive Words in Reasoning. If we imagine a set of true statements, then a statement is either true or false, with no gradations of truth.
Fuzzy mathematics defines a different kind of set, and a different measure of truth.
If we define a fuzzy set of true statements, a real statement will belong to the set more or less depending on how true the statement is. A member of a fuzzy set has a grade of membership indicating how sure we are that the member belongs to the fuzzy set. For a particular subject, the confidence in each symptom represent the confidence that the subject really has that symptom. One important advantage that fuzzy sets offer to constructors of expert systems is the ability to work in terms of familiar words. Typical fuzzy sets are shown in Table 1.