Define subjunctive and give example.

Subjunctive is a grammatical mood that expresses various states of unreality such as wish, doubt, possibility, necessity, requirement, and action that has not yet occurred. It typically involves the use of a verb form that differs from the indicative in morphology and syntax.

Example: If I were a bird, I could fly. (the subjunctive verb form "were" is used instead of "was" to express an unreal or hypothetical situation)