How does Conor McPherson use the ghost stories to explore the key themes of the play?

In the play The Weir, Conor McPherson uses supernatural stories to showcase the rich literary history and oral traditions of Ireland. Many of the tales the characters recount have an element of Irish folklore or mythology. In this sense, the stories conjure the past—both the history of Irish culture and personal histories.
The other subtext of the play is how the past "haunts" the characters. This is especially true for Valerie and Jack. Valerie tells the other people in the pub why she left Dublin. This is in line with the theme of escaping a past that haunts them. Likewise, Jack offers a non-supernatural story but states that it is about a haunting nevertheless.
McPherson does a brilliant job of using the context of ghost stories to create an analogy for the true message of his play. McPherson tells us that ghosts are not just supernatural beings, but "past lives" and memories as well.
http://dergiler.ankara.edu.tr/dergiler/13/1937/20301.pdf