*A verb in subjunctive mood can express a wish.
Example: God bless you.
Long live the Queen.
Note the use of simple tense without any conjugations, here.
*A verb in subjunctive mood makes statements of impossibilities and improbabilities.
If I were the President of U.S., I would have stopped the attacks on civilian targets.
ObservationMy becoming the President of U.S. is an impossibility.
Note the use of the plural-past-supporting-verb "were" for the first person I.
It is not clear, who first started the use of plural-past-supporting-verb "were", in subjunctive mood. It unnecessarily confuses users, because 'were' is a supporting verb which indicates past tense.
"I shall stop the attacks on civilian targets, if I am the President of U.S."
"I would have stopped the attacks on civilian targets, if I was the President of U.S."
The above sentences would have also been correct, had English been a logical language. English occasionally throws away logic into garbage dump.
See the following statement:
I shall donate one dollar, if I get ten dollars.
The mood is not subjunctive here. Reason: I have a probability or possibility of getting ten dollars. It is not impossible. I have, hence, used the right tense i.e. the future tense "I shall donate". "If" when used in conditions, is normally followed by a verb in simple present tense.
SOME QUOTES OF IMPOSSIBILITIES
I have more memories than if I were a thousand years old. ? Charles Baudelaire.
If I were a girl , I'd despair. The supply of good women far exceeds that of the men who deserve them. ? Robert Graves.
If I were a grave-digger or even a hangman, there are some people I could work for with a great deal of enjoyment ? Douglas Jerrold.
If I were a writer, how I would enjoy being told the novel is
dead? Don Delillo.
If I were a man I wouldn't bother to change while there are women like that around. ? Ann Oakley.
If I were a man I would always be laughing at myself. ? Yoko Ono.
If I were a side dish , he hadn't ordered. ? Ring Lardner.
If I were a woman I would kiss as many of you as had beards that
pleased me, complexions that liked me and breaths that I defied not ?
I would want him to do everything for me and wait on me as
if I were a princess. But that is not the way at all. ?
If I were a piece in a game of chess, when my opponent says of it: That piece cannot be moved. ? Soren Kierkegaard.