When your chosen themes accommodate one another, you can create a unifying theme. Consider 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 with your living room; this is sort of a miniature version of Disney's Epcot. You could potentially incorporate Asian tropic samurai, plants and dragons swords that would incorporate all three themes. The idea is, regardless of the themes, there is certainly common ground to be found.