I think in fact it would be safe to say that, besides some fairly simple prerequisites, there is not a lot in the way of 'official' teachings on ghosts. That leaves a lot of room for speculation, as long as we remain firmly grounded in Catholic doctrine. For instance, we accept that the soul is created by God and does not pre-exist. We accept that all humans are judged at their death without exception, that some go to hell, some to heaven, and some heaven by way of purgatory.
These things in mind, I think it may be fun to look into some of the speculative theology and speculation in general surrounding ghosts and other paranormal phenomena from a Catholic perspective. I'll start with a nice old book I picked up called Ghosts and Poltergeists by Fr. Herbert Thurston, a Jesuit priest who died in 1939. It mainly deals with poltergeist activity, and is heavily focussed on individual accounts.
A General View of Poltergeist Phenomena
[Part I, pages 1-4]
Although the Herman world "poltergeist" is now naturalized, and is often met with in the newspapers of both England and America, still an examination of standard dictionaries shows that it is a term of comparatively recent introduction. Few, if any, of those published in the last century will be found to contain in, and it is particularly noticeable that it is not recognized by The Stanford Dictionary of anglicized words and phrases (London, 1892), though this work was expressly compiled to registered those foreign importations into the language which had acquired rights of citizenship. The word does appear in the great Oxford English Dictionary in 1910, but the earliest illustration there given of its use dates only from 1871. It is certainly older than that. Mrs. Crowe, in her widely-circulated book The Night Side of Nature (1848), makes frequent use of it - once in a chapter heading. When the Spiritualistic movement started in America, more attention was naturally directed to such matters, but the earliest American example I have met of the use of this term occurs in an article copied in 1852 from the Boston Pilot which speaks as follows:
The Germans have long been familiar with a mischievous devil called the "Polter geist" whose delight it appears to be to enter houses and turn everything upside down, doing more mischief in an hour than a thousand monkeys would do in a day. It is not well to listen to these things, but really some respectable witnesses have testified that this same monkey ghost has troubled several families in England and America within the last few years.
The article was reproduced in a book Spiritual Manifestations, by Adin Ballou, which may claim to be the first systematic treatise on Spiritualism ever printed either in America or elsewhere. As Ballou's little volume went through several editions, and was republished on both sides of the Atlantic, appearing in London, and again in Liverpool, within less than twelve months, it may very easily have helped to give currency to a term previously unfamiliar to most writers of English. Moreover, the description supplied may be regarded as fairly accurate. A poltergeist is simply a racketing spirit, which in almost all cases remains invisible, but which manifests its presence by throwing things about, knocking fire-irons together and creating an uproar, in the course of which the human spectators are occasionally hit by flying objects, but as a rule suffer no serious injury.
In the last century several prominent members of the Society for Psychical Research - notably Mr. Frank Podmore from the sceptical standpoint and Mr. Andrew Lang in a more benignant vein - occupied themselves with poltergeist phenomena; but the most important contribution to the subject, definitely upholding the objective reality of these manifestations, is that published in 1911 by the late Sir William Barrett, F.R.S. Being himself then resident in Ireland, he had personally investigated two Irish cases, and he takes occasion to outline the features which are found to recur in other examples of the same type of disturbance gathered from all parts of the world. The points upon which he lays stress as characteristic of the poltergeist are the invisibility of the agents, the sporadic and temporary nature of the manifestations, and notably their dependence upon the presence of some particular individual - usually a young person and often a child - who must be assumed to possess strange, if unconscious, mediumistic powers. When telekinetic phenomena occur - and this is almost invariably the case - whether they take the form of missiles which seem to come from nowhere, or of crockery and even furniture crashing or flying through the air, the movement often seems to be controlled, tortuous and at variance with the laws of gravitation. Professor Barrett writes: -
The movement of objects is usually quite unlike that due to gravitational or other attraction. They slide about, rise in the air, move in eccentric paths, sometimes in a leisurely manner, often turn round in their career, and usually descend quietly without hurting the observers. At other times an immense weight is lifted, often in daylight, no one being near, crockery is thrown about and broken, bedclothes are dragged off, the occupants sometimes lifted gently to the ground, and the bedstead tilted up or dragged about the room. The phenomena occur both in broad daylight and at night. Sometimes bells are continuously rung, even if all the bell wires are removed. Stones are frequently thrown, but no one is hurt; I myself have seen a large pebble drop apparently from space in a room where the only culprit could have been myself, and certainly I did not throw it. [Proceedings of the Society for Psychical Research, Vol. XXV, p. 378.]
In both the cases investigated by Professor Barrett, rappings and inexplicable noises played a prominent part. The earlier occurred in 1877 at a lonely hamlet called Derrygonnelly, nine miles from Enniskillen, in the house of a farmer who had been left a widower with a family of four girls and a boy, the eldest child, Maggie, aged about twenty, seeming to be the centre of the disturbance. Strange rappings and scratchings were first heard, then objects were seen to move, stones began to fall, and candles and boots were repeatedly thrown out of the house. Several neighbours urged them to send for the priest, but the family were Methodists and preferred to put an open Bible on the bed with a big stone on top of it. Some unseen power, however, displaced the Bible and eventually removed it from the room, tearing seventeen pages right across. The freakish disturber of their peace evinced a peculiar dislike for any source of artificial light; candles and lamps were mysteriously stolen or thrown out, and Professor Barrett recounts how the old farmer told him that "Jack Flanigan came and lent us his lamp, saying he would engage the devil himself could not steal it, as he had got the priest to sprinkle it with holy water." Nevertheless the lamp, in spite of the blessing, seems to have shared the fate of the Bible. When Professor Barrett visited the scene he heard the long continued knockings some of which were "like those made by a heavy carpenter's hammer driving nails into flooring." He satisfied himself that the noises could not have been made by any of the inmates, who were all in view, and, as already mentioned, he saw a stone fall from the void. Moreover he challenged the mysterious agent of the knockings to echo by raps the numbers which he mentally indicated; which is did. Further putting his hands into the side pockets of his overcoat, Professor Barrett asked the spirit to "knock the number of fingers he held open." The experiment was repeated four times, with varying numbers, and in each case the answer was given correctly.
The disturbances which took place at Enniscorthy in July, 1910, were more dramatic, and though in this case Professor Barrett was not personally a witness of the phenomena, still the depositions he obtained from those principally concerned are so explicit and so fully confirmed by independent testimony that it would be unreasonable to doubt the facts. Apart from hammering and other noises, the prank upon which the poltergeist seemed to concentrate his efforts was the pulling off the bed-clothes and the moving right across the floor of a heavy bedstead, which, lacking one castor, was a particularly difficult object to shift from its place. Three young men slept in the room, all of whom were reduced to a state of abject terror. The principal sufferer was a lad of eighteen, named Randall. According to his account, confirmed on one occasion by reliable investigators who sat up with them, the sheets and blankets were pulled off him, he himself was dragged out of bed on to the floor, "a chair danced out into the middle of the room without anyone near it," and when all three in their fright decided to get into one bed together, "the bed turned up on one side and threw us out on to the floor, and before we were thrown out, the pillow was taken from under my head three times. When the bed rose up, it fell back without making any noise." [Proceedings S.P.R., Vol. XXV, p. 389.]
I intend to post more of this over time, in pieces around this size.