Is there an in-game reason for the exclusivity of supernatural templates in the new World of Darkness? (Why can't a werewolf or a vampire awaken and be a mage as well, for example?) If there is, where do I find it?
(If I ever read such an explanation, I've completely forgotten about it.)
Best Answer
Supernatural power comes from making mutually exclusive changes to the human soul.
My view isn't explicitly stated anywhere, but I consider it supported by statements across the nWoD books. There are a few representative quotes from the core books I own at the bottom.
To do anything majorly supernatural, you need to be more than human. A vampire's soul is deadened and blended with the Beast from his sire's vitae. Werewolves are born with a soul that is supernaturally potent but sleeping for years. Mages awaken and gain sympathy between their souls and the Realms Supernal. Changelings are torn, mangled and blended with Fae stuff.
None of these changes can coexist in one person. Taking a Mage for an example. If you aren't a normal mortal, then you cannot be in close enough sympathy with the supernal realms to perform magic.
From Vampire The Requiem 181
From Werewolf the Forsaken Page 75
From Mage the Awakening Page 32
From Changeling the Lost Page 24
and