The subjunctive mood is the verb form contrasted with the indicative and imperative moods. It occurs somewhat oddly in English because in many persons and tenses, the same form is
used for indicative and subjunctive verbs. It is used primarily to express events that are contrary to
fact or, if
set in the
future tense, uncertain. This is why one says "If I were..." instead of "If I was..." though the latter is not always incorrect. The conditional word "if" often introduces a contrary to
fact or uncertain condition, but it can also express a certain condition (usually when it could be replaced with "when") thus: "If it were raining, I would be happy" versus "If it was raining, I was happy." The verbs of the first are in the present tense and subjunctive mood, the
second in the past tense and indicative mood. The first expresses the idea that if it were raining (but it's not), I would be happy (but I am not happy). The
second expresses the idea that whever in the past it was raining, I was happy. Subjunctives are also used to express hortitory and jussive ideas such as "God save the
queen." Using the subjuctive, one says "It is imperative that he read this" rather than "It is imperative that he reads this," but it is
never used with the "that" of indirect statement. The subjunctive mood is rarely used or correctly formed in conversational English (and many
popular works of literature).
Incorrect: If I was rich, I would not live in a
box.
Correct: If I were rich, I would not live in a
box.