What is a house, really?

Matthew Yglesias is killing it in a series of three posts (one, two, three) about the fact that McCain doesn’t know the number of houses he owns. I assumed McCain was just poorly dodging the question, but after reading Yglesias it occured to me, for the rich like McCain, answering such a question can be a serious meditation on mereology. Does the two condos McCain bought and later joined together count as one property or two? Does his ranch with six buildings count as one property or 6? Or some number in between reflecting, say, the places that have bedrooms? These are serious questions that may have no integer solution but instead some safe confidence interval.