Breakdown of Ihr plant die Party um, es sei denn, der Biergarten hat ein Dach.
ein
a, an (eine)
haben
to have
ihr
you (informal plural)
die Party
the party
Questions & Answers about Ihr plant die Party um, es sei denn, der Biergarten hat ein Dach.
Why is the verb hat in the second position after es sei denn? Shouldn't it go to the end?
The phrase es sei denn is special because it is followed by a normal main clause where the conjugated verb stays in position 2. If you want to put the verb at the end, you have to add dass to make it a subordinate clause: es sei denn, dass der Biergarten ein Dach hat. Both versions mean exactly the same thing.
Where does the um in Ihr plant die Party um come from?
It is the separable prefix of the verb umplanen (to reschedule or replan). Since this first part of the sentence is a main clause, the conjugated verb (plant) is in position 2, and the prefix (um) is pushed to the very end of its clause, right before the comma.
Could I use außer wenn instead of es sei denn?
Yes, außer wenn also means 'except if' or 'unless' and is very common in everyday speech. Just remember that wenn is a subordinating conjunction, so it kicks the verb to the end of the sentence: ..., außer wenn der Biergarten ein Dach hat.
Why is the word sei used here? Is that subjunctive?