From a book on Exorcism:
Most pagan societies believe in the separation of the soul from the body and an afterlife. This includes the idea that souls may “linger” after death due to “unfinished business” such as unbroken attachments to the earth, to unreconciled relationships or to the affairs of men that supposedly last beyond the grave. In this view, the souls can be benign or malicious; often pagan traditions of ancestor worship or appeasement of the dead are the result of these beliefs.
"The Roman Catholic belief is categorically different from these pagan beliefs, however. The theological tradition concerning souls in purgatory is based on the belief that bodily death constitutes a definitive entrance into an afterlife which is either a temporal purification followed by heaven, or an eternal damnation. Thus, for Catholics there is no such thing as a “lingering” or “wandering” soul who has “not cut the bonds of this earthly life.” For Catholics, there is another way to explain these things than the standard pagan reasoning.
"A strong theological tradition recognizes that deceased human souls can and do visit the living after death for various reasons and in various modes. It is clear that this is only done “according to the disposition of Divine providence” and not as a common occurrence. St. Thomas Aquinas says that “separated souls sometimes come forth from their abode and appear to men…”, and this can be both for “intimidation” (i.e., damned souls) or for “instruction” (i.e., redeemed souls). He also claims that souls may appear to others “in order to seek our suffrages” (i.e., souls in purgatory). Such apparitions can also be due to a special intervention into the human sphere by a demon creating a deception or an angel appearing in human form to communicate a message.
"Some people call these various apparitions “ghosts.” In light of the tradition above, these can be either disembodied human souls or evil spirits. In Catholic thought, however, if such appearances happen, they are always limited and marked by truth, simplicity and utter clarity to distinguish a holy apparition from a demonic one, which is always marked by confusion, discord, chaos, fear and anxiety. Thus, there is no strictly theological basis for believing that there are souls “wandering” around in the world communicating with loved ones, or “haunting” places, but Catholics do believe that the deceased can appear after death in a strictly limited fashion and only with God’s permission for some greater reason.
“What has been absolutely forbidden by the Church from the beginning is the attempt to conjure deceased souls from the grave or to communicate with the dead, a dark art known as necromancy. This prohibition is from Scripture. In the Christian tradition, we honor the dead and pray for them- we even consider ourselves in communion with them- but we do not conjure them up or attempt to dialogue with them. All such practices open us up to demonic deception and infestation.”
