Circumscription (logic)
Circumscription is a non-monotonic logic created by John McCarthy to formalize the common sense assumption that things are as expected unless otherwise specified.
Contents
Description
Circumscription was later used by McCarthy in an attempt to solve the frame problem.
To implement circumscription in his initial formulation, McCarthy augmented first-order logic to allow the minimization of the extension of some predicates, where the extension of a predicate is the set of tuples of values the predicate is true on. This minimization is similar to the closed world assumption that what is not known to be true is false.
Original problem
Missionaries and cannibals
The original problem considered by McCarthy was that of missionaries and cannibals:
- There are three missionaries and three cannibals on one bank of a river
- They have to cross the river using a boat that can only take two
- With the additional constraint that cannibals must never outnumber the missionaries on either bank, as otherwise the missionaries would be killed
= Excluding conditions that are not explicitly stated
The problem considered by McCarthy was not that of finding a sequence of steps to reach the goal (the article on the missionaries and cannibals problem contains one such solution), but rather that of excluding conditions that are not explicitly stated.
See also
External links
- Circumscription (logic) @ Wikipedia
