Your urban fantasy automatically takes place in an alternate universe, because the existence of supernatural and magical items would alter society fundamentally. At least, that's what Bill Willingham, Jon Courtenay Grimwood and other panelists at World Fantasy 2009 claimed.
The "Urban Fantasy As Alternate History" panel at WFC 2009 made a compelling case that you can't introduce magical elements to a present-day world, or to the history of a present-day world, without all of the social institutions being rearranged. Besides Willingham and Grimwood, the panel included Paul Park, L.E. Modesitt, and Michael Swanwick. Among other things:
- If magic was real, it would be illegal. Or else, it would be regulated and taxed.
- If ghosts were real, as in Modesitt's novels, all sorts of institutions would change — women who died in childbirth would hang around, and the birth rate would probably go down.
- There would be civil rights movements for ghosts and the undead — and if they could vote, they would probably a majority.
- There would be whole new careers and economic sectors associated with magical and fantastical creatures.
Most of all, people in these "urban fantasy" worlds would take for granted many things that would shock us utterly. Says Willingham, "In my world, vampires are real, and they're just part of society." Adds Swanwick: "Gorillas used to be cryptobiology," until they became commonly known.
"There's kind of poignancy in the prosaic state," says Park.
Swanwick praised Rachel Pollack's Unquenchable Fire, in which shamanistic magic has pervaded "our" world, and now daily mouse sacrifices are required to keep your electricity on, and there are parades with bare-breasted cheerleaders with blood running down their faces. "It's prosaic and ordinary to everyone else, but absolutely strange to us, the reader."
Anticipate lots of weird legal questions if the supernatural became part of everday life — like, if a vampire "turns" you, is that murder? Or maybe a jury would rule that the vampire is actually giving the "victim" a gift: eternal life. Or maybe it's theft, because the vampire is robbing you of the promise of death. If you believe in Christianity, is the vampire robbing you of the possibility of salvation in the afterlife? Is a newly turned vampire a new person, with no existing property rights, or does he/she keep all the property from his/her life? The lawyers, as they say, would have a field day.
"Legal fictions are every bit as fantastic as magic, and yet they wield the same power," says Swanwick.