Question Six of Chapter Three of the Third Decade
That one must not believe a possessed person who says that he is the spirit of someone deceased
It is asked whether a possessed person is to be believed when he says that he is the soul or spirit of someone deceased.
To this it is answered that in no way are possessed persons who say that they are the souls of the dead to be believed, as has occurred rather often at Rome in Saint Peter’s at the iron-bound Column of Solomon.
For such beings are truly demons, who frequently pretend that they are souls of the dead in order to confirm the error of the gentiles, who believed this, as Augustine adduces concerning Hermes in Book X of The City of God, and as Chrysostom says upon Matthew.
These things are from Thomas, First Part, question 117, article 4, reply to the second objection.
And if they sometimes say certain true things which those damned souls whom they claim to be did during life, faith is not to be placed in them.
For such beings are not the souls of those persons but demons, and perhaps those very demons whom the souls possessed during life as their inciters and for their exercise, dwelling in the higher murky air. For in the common course such demons are accustomed to vex the bodies of human beings.
Or they are other demons which learned the things they reveal from the demons that tempted and conquered those souls during life.
These things are from the theologians and from those cited above.
Addition
Perhaps the spirits which say to a possessed person that they are the soul of some man or woman are, as the author also says, either the spirits which once used to tempt those persons, or spirits so mingled with those evil tempting spirits that they have been made one and the same.
Thus Christ intimates concerning the soul of Judas when he says: “One of you is a devil,” on account of a certain union, as it were, arising from sin.
For just as Christ united the Church to himself through faith and the sacraments in a mystical unity, so the devil unites the evil to himself through sin.
Souls therefore do not transmigrate from bodies into bodies, as Plotinus appears to think. Rather, these things are mere fictions of the gentiles and poets.
Eusebius also says certain things concerning them in Book IV of The Preparation for the Gospel, chapter 11.