x will be true if y doesn’t happen; x won’t be true if y does happen;

I’m going to break your legs unless you pay me.

Nobody can come in unless their name is on the guest list.

I’ll do it, unless anyone here has a problem with that.

Dave knew that unless he found some money quickly, he would lose the house.

You two shall be married, unless anyone here can think of a reason why this should not come to pass.