Pete didn't wear a coat. He didn't expect it to be cold. Had Pete.......
Had Pete known it was so cold, he would have worn a coat.
You may need help filling out the application. Give me a call if you do. Should.......
Should you need help filling out the application, give me a call.
You didn't tell me it was a casual dinner. I'm wearing my dinner jacket. Had you told me.......
Had you told me it was a casual dinner, I would have worn something else.