For most verbs, the subjunctive (expressing wishes, recommendations, indirect requests, and speculations) differs from the indicative (statements of real things, or highly likely ones).

In the subjunctive, we use the plural form for the third-person singular. (“He takes” in the indicative becomes if “he take”in the subjunctive.)

For “to be” verbs in the subjunctive, we use:

• “be” in first- and third-person forms of the present tense (“she is” becomes “if she be”).
• “were” in first- and third-person forms of the past tense (“I was” becomes “if I were”).
• “have been” in first- and third-person forms of the present perfect tense  (“he has been” becomes “if he have been”).
(It all sounds kind of funny out of context. The examples below should clear it up.)

The subjunctive mood isused in these instances:

1. In “if” clauses to express condition contrary to fact.

Examples:

“If I were a rich man…”
“Were he alive, he would be proud of his son.”

2. In “that” clauses expressing a wish, request, recommendation or report of a command.

Examples:

The president requested that the emissary be treated fairly.
The attorney general demanded that the Congress come to a decision immediately.
The committee recommended that the rules be changed.

3. In main clauses to express a wish, hope, prayer, request or recommendation.

Examples:

I wish I were still living in Minnesota.
Hallowed be thy name.
Heaven help the working woman.
Long live the Queen!
The subjunctive be hanged!

A warning: Just because a sentence starts with “if” doesn’t mean it’s necessarily improbable or contrary to fact.  “If” sometimes introduces clauses of logical possibility, supposition or concession, and those are in the indicative mood. (“If Joe Biden was president….” Not likely, but certainly a possibility.)