conj.if; in case; supposing
If she does not show up, we'll go and find her.
If I were him, I wouldn't have done it that way.
If I had known then I wouldn't have come.
If a poet is divorced from the hustle and bustle of life, he can't write inspiring poetry.
If it were me, I wouldn't go.
She would have cracked up if she hadn't allowed herself some fun.
You would know what was going on if you'd listened.