Default Reasoning
An example of a default assumption is that the typical bird flies. As a result, if a given animal is known to be a bird, and nothing else is known, it can be assumed to be able to fly. The default assumption must however be retracted if it is later learned that the considered animal is a penguin. This example shows that a logic that models default reasoning should not be monotonic. Logics formalizing default reasoning can be roughly divided in two categories: logics able to deal with arbitrary default assumptions (default logic, defeasible logic/defeasible reasoning/argument (logic), and answer set programming) and logics that formalize the specific default assumption that facts that are not known to be true can be assumed false by default (closed world assumption and circumscription).
Read more about this topic: Non-monotonic Logic
Famous quotes containing the words default and/or reasoning:
“In default of inexhaustible happiness, eternal suffering would at least give us a destiny. But we do not even have that consolation, and our worst agonies come to an end one day.”
—Albert Camus (1913–1960)
“If death, said my father, reasoning with himself, is nothing but the separation of the soul from the body;—and if it is true that people can walk about and do their business without brains,—then certes the soul does not inhabit there. Q.E.D.”
—Laurence Sterne (1713–1768)