What Are the Ghosts of the Underworld?

The dead know things that we don't for reasons which are not entirely clear and they can say more about that. The ghosts of young women who never got married are often are very common, because presumably because they never attained the full range of living human motherhood. They're seen as fundamentally lacking as opposed to a living person. And what kind of purposes are they exploited for? Well, the two obvious ones would be necromancy, divination from the dead.