Distinction between kinds of truth. Necessary truth is a feature of any statement that it would be [logically] contradictory to deny. (Contradictions themselves are necessarily false.) Contingent truths (or falsehoods) happen to be true (or false), but might have been otherwise. Thus, for example:
“Squares have four sides.” is necessary.
“Stop signs are hexagonal.” is contingent.
“Pentagons are round.” is contradictory.