How can Cole's mother talk to Bruce Willis if he's one of Cole's ghosts?

In the 1999 movie 'The Sixth Sense' starring Bruce Willis, if Cole Sear is the only person to be able to 'see dead people' how can Cole's mother, Lynn Sear have a conversation with Bruce Willis? You only find out Bruce Willis is a ghost at the end, but he gets shot in the first scene, so in essence Bruce Willis is........a ghost......