Negations, Negations are a statement that asserts an opposite of a statement

Converse, switches the if and then in a statement If a polygon is a quadrilateral then it has exactly four sides If a polygon has exactly four sides, then it is a quadrilateral

Inverse, negate both statements If a polygon is a quadrilateral then it has exactly four sides If a polygon is not quadrilateral then it does not have exactly four sides

Contrapositive, both of the latter two statements Contrapositive statements are always true