if

If it rains, I shall get wet.

If A, then B, else C.

I would prefer it if you took your shoes off.

If that's true, we had better get moving!

He was a great friend, if a little stingy at the bar.

I don't know if I want to go or not.

“Wait a minute!” said the girl: “I wouldn’t hurry by, if it was you that was coming out to be hung, the next time eight o’clock struck, Bill. I’d walk round and round the place till I dropped, if the snow was on the ground, and I hadn’t a shawl to cover me.”

I have leftover cake if you want some.