Contingency (Encyclopedia of Science and Religion)
A proposition is necessary when there is no possible case in which it is false ("a vixen is a female fox"). A proposition is contingent when it is true in some cases and false in others ("it is raining now"). By extension, a state of affairs is contingent if it could have been other than it is. A state of affairs is necessary if there is no possible alternative to it. Most philosophers think that all physical states are contingent. Some physicists argue that the universe has to exist, whereas some theologians argue that God has to exist, but creates a contingent universe.
See also CHANCE