When your chosen themes accommodate one another, you can create a unifying theme. Look at this: your spouse wants an Asian theme, your teenage daughter wants a gothic theme and you want a tropical theme. In such varied combination you may decide to do an around-the-world theme inside your living room; this is sort of a miniature version of Disney's Epcot. You could potentially incorporate Asian tropic dragons, samurai and plants swords that would incorporate all three themes. The point is, regardless of the themes, there may be common ground available.