I don't believe or disbelieve in ghosts - anything in this world is possible. All I know is that I've never seen one.
That said, my daughter insists her house has a ghost. It's over 100 years old, and when she and her husband bought it, there were several tombstones lying around in the back yard. She did some research and found that one of them was engraved with the name of a child whose family was the house's original owner. Both she and her husband, as well as their kids, claim to occasionally see "Mary" moving around.
Even stranger, when they were touring the house with the Realtor years ago, their oldest child was about 5. She came down from the upstairs and told my daughter that ". . . the little girl upstairs told me that we should buy this house."
"The great object is, that every man be armed. Everyone who is able may have a gun." - Patrick Henry