Contingency in Philosophy is a state where something could be either true or false. It is not normally an issue in propositional or first-order logic, but in modal logic, there is an important distinction there. Contingency of formulae is universally important, as it distinguishes normal formulae from tautologies and contradictions. It is deemed necessary or impossible depends almost entirely on time and perspective. It is also an alternate plan in case a previous expected event does not occur.
