In
logic, a
many-valued logic (also
multi- or
multiple-valued logic) is a
propositional calculus in which there are more than two
truth values. Traditionally, in
Aristotle's
logical calculus, there were only two possible values (i.e., "true" and "false") for any
proposition. Classical
two-valued logic may be extended to
n-valued logic for
n greater than 2. Those most popular in the literature are
three-valued (e.g.,
Lukasiewicz's and
Kleene's, which accept the values "true", "false", and "unknown"), the finite-valued (finitely-many valued) with more than three values, and the infinite-valued (infinitely-many valued), such as
fuzzy logic and
probability logic.