Four statements driven from the original: converse: if a pair of angles are congruent, then the angles are vertical. inverse: if a pair of angles are not vertical, then the angles are not congruent. contrapositive: if a pair of angles are not congruent, then the angles are not vertical. conditional: if a pair of angles are vertical, then the angles are congruent. b) If you know that a statement is true, then its contrapositive form must be true as well.