
The Theory of Fuzzy Sets 277
torn-off roofs and downed power lines, they inform the audience that the storm was
a “real bad one,” or “yesterday was a beautiful day, if you’re a duck.” These are ways
of saying that, as storms go, this was a real storm: Its membership in the set “storms”
was very high. Probability is meaningless, but fuzzy set membership continues after
the event.
Other important differences exist between fuzzy logic and probability. Prob-
ability is based on a closed world model in w hich it is assumed that everything is
known: Fuzzy logic is not based on that model and makes no such assumption. Prob-
ability is based on frequency (Bay ...