In real world, there exists much fuzzy knowledge; Knowledge that is vague, imprecise, uncertain, ambiguous, inexact, or probabilistic in nature.
Human thinking originating from and reasoning inherently frequently inexact human involve fuzzy concepts. information, Humans, can give satisfactory answers, which are probably true.
However, is, our systems most systems are unable to answer many questions. The reason designed based upon classical
set theory and two-valued logic which is unable to cope with unreliable and incomplete information and give expert opinions.