As there is much confusion out there on this subject, here is some information from an expert on this subject. Commentary later today.
What is possession? By possession the devil really dwells in the body of the victim, instead of only making his action felt from the outside, as in obsession. Moreover, by thus acting from within, he not only hinders the free use of a man's faculties, but he himself speaks and acts by the organs of the possessed person, without the latter being able to hinder him from doing so, and even as a rule without his perceiving it.
When we say that the devil dwells in the body of a person, we do not mean that he is there like the soul itself which informs the body, but like a motor which, through the body, acts on the soul. He acts directly on the members of the body, makes them execute all sorts of movements, and he acts indirectly on the faculties in the measure in which they depend on the body for their operations.
Two states are distinguished in possessed persons: a state of crisis, with contortions, outbursts of rage, blasphemous words; and a state of calm. During the crisis, the patient generally loses, it seems, the feeling of what is taking place in him, for afterward he has no memory of what the devil has, they say, done through him. Nevertheless, as an exception, there are possessed persons who remain aware of what is taking place in them during the crisis. This was, it seems, the case with Father Surin, who, while exorcising the Ursulines of Loudun, himself became possessed or at least obsessed. He said: "In this state, there are very few actions in which am I free." (10)
In the state of calm, the devil seems to have withdrawn, although there may still remain at times chronic infirmities which physicians do not succeed in curing.
As a rule possession is more properly a punishment than a purifying trial. However, there are exceptions, like the case of Father Surin, that of Blessed Eustochium of Padua, beatified by Clement XIII, on March 22, 1760,(11) that of Marie des Vallees, spiritual daughter of St. John Eudes.(12) Mention must also be made of the more recent case of Sister Mary of Jesus Crucified, an Arabian Carmelite who died in the odor of sanctity at Bethlehem in 1878, and the cause of whose beatification has been introduced. She was twice the victim of possession, or at least of a very strong obsession, first at the Carmel of Pau, later at that of Mangalore.(13) There have been other similar cases, in which possession was a concomitant phenomenon of the passive purification of the senses or that of the spirit, in souls that offered themselves as victims for sinners.
What are the signs of real possession? Great care must be taken to distinguish it from certain cases of monomania and of mental alienation which resemble it. According to the Roman Ritual (De exorcizandis obsessis a daemonio), there are three principal signs: "To speak an unknown language, making use of several words of this language or understanding him who speaks it; to disclose distant and hidden things; to manifest strength which surpasses the natural powers of the subject, considering his age and state. These and other similar signs, when united in great number, are the strongest indications of possession." They are particularly striking, for example, if a person who does not know either Latin or theology or knows only their rudiments, speaks in correct and even elegant Latin about the most difficult problems of theology, like that of the gratuity of predestination.(14) It is true that people adduce cases of morbid exaltation which awaken in the memory forgotten languages or fragments that have been heard; but in this question the Ritual demands much more, as we have just seen. Accompanying possession at times is levitation, a preternatural phenomenon which manifests itself under circumstances of such a nature that they cannot be attributed to God or to the good angels, but must be attributed to the devil. According to tradition, this was the case with Simon Magus who, they say, was lifted into the air and fell down.
Another indication of possession is that on coming into contact with a sacred object or on the recitation of certain liturgical prayers, the person believed to be possessed becomes furious and blasphemes horribly. This sign is more significant when the experience is brought about without the knowledge of the person, in such a way that the reaction is not produced by him, by his ill will, or by a desire to simulate possession.
It has been pointed out, apropos of these signs, that in extreme hysteria there are analogous phenomena.(15) Analogous, it is true, but not specifically similar; in hysteria the patient does not discourse in a language of which he is ignorant and in a learned manner on problems of which he has no knowledge at all, such as predestination or the efficacy of grace. Besides, the devil can produce either nervous diseases, or exterior phenomena analogous to those of neuroses; he may also make use of an existing illness and reduce the patient to a state of exasperation.
What are the remedies for possession? The Ritual indicates the following: (I) The possessed person must do penance and purify his conscience by a good confession. (2) He should receive Holy Communion as often as possible, according to the advice of a prudent and enlightened confessor. The more pure and mortified a soul is, the less hold the devil has on it; Holy Communion introduces into the soul the Author of grace who is the conqueror of Satan. However, Holy Communion should be given only in moments of calm. (3) The possessed person should often implore the mercy of God by prayer and fasting. (4) With a great spirit of faith he should make use of sacramentals, in particular of the sign of the cross and holy water.(16) He should have trusting recourse to the invocation of the holy name of Jesus, of His humility, His immense love. (5) Lastly, the exorcisms were instituted for the deliverance of possessed persons in virtue of the power of driving out devils which Jesus Christ left to the Church. But solemn exorcism may be performed only by priests chosen by the bishop of the place and with his special authorization.
The Ritual counsels exorcists to prepare themselves for this difficult function by prayer, fasting, and a humble and sincere confession, so that the devil may not reproach them with their own sins. In addition, solemn exorcism should, at least as a rule, be performed only in a church or chapel. The exorcist should be accompanied by grave and pious witnesses, sufficiently strong to overpower the possessed person if necessary. Lastly, the exorcist should proceed to the interrogations with authority, rejecting all that is useless. He summons the devil or the devils to declare the reason for the possession and to tell when it will end. To oblige the enemy of God to do this, the exorcist must redouble the adjurations which seem to irritate the devil most, that is, the invocations of the holy names of Jesus and Mary. If the evil spirit makes sarcastic and derisive answers, silence must be imposed upon him with authority and dignity. The witnesses should be few in number, they must not ask questions, but should pray silently. The exorcisms should be continued for several hours and even for several days, with intervals of respite, until the deliverance, which should be followed by prayers of thanksgiving.
Many authors point out that the exorcisms are not always efficacious against obsession. They do not deliver the soul completely from an obsession which is part of the passive purifications, for God permits it for a time known to Him, in view of the great advantages which the soul should derive from this trial.
We have studied particularly the diabolical vexations which Sister Mary of Jesus Crucified had to undergo in 1868 in the Carmel of Pau and in 187I in that of Mangalore, not only according to the account given by Father Estrate in her Life and the shorter report by Father Buzy, but also according to the testimony gathered by her directors and superiors. We are convinced that in her case there was, on two different occasions, possession or at least a strong obsession which took away from the servant of God the responsibility for certain exterior acts (a short departure from the cloister, which was not yet canonically established) and for certain remarks contrary to humility and obedience, virtues which she practiced in a heroic degree, even in those obscure periods, as soon as she recovered the use of her faculties.(17)
We think there was in this case not a punishment, but a trial and very great merit. As Father Estrate,(18) who was one of the directors of this valiant Carmelite, points out, she bore these diabolical vexations with heroic patience, a very great spirit of faith, an admirable confidence in God, an ardent love of God and of souls. As long as she preserved freedom of movement and the use of speech, she spent hours at a time replying to all the suggestions of the devil. The devil had permission to attack her one hundred times in the Carmel of Pau, and he sought by every means to make her utter a complaint; "always conquered, he begged the Master to be allowed not to continue the struggle. Jesus obliged him to go on." The servant of God did not cease to reply to his assaults by words such as these: "I offer my sufferings for the enemies of Jesus, that they may love Him as St. John did." The devil was forced to say: "Do you know why the little Arab speaks thus? Why is she strong? Because she walks in the steps of the Master." At length at the end of forty days she was freed.(19)
This case furnished an example of one of the greatest trials which may accompany the passive purifications of the senses or the spirit. It brings out strikingly the truth of what St. John of the Cross says on this subject: "There is open warfare between two spirits. . . . This attack of the devil takes place also when God bestows His favors upon a soul by the instrumentality of a good angel. The devil sees this occasionally, because God in general permits it to become known to the enemy, that he may do what he can [that is, if God grants the soul extraordinary favors, He often permits the devil to fight as if with equal arms, by extraordinary vexations]. . . . At that time the mental agonies are great and occasionally surpass all description; for when spirit has to do with spirit, the evil one causes an intolerable horror in the good one." (20) All authors of mystical theology express the same opinion, and there are similar facts in the lives of many canonized saints.
The example we have just recalled and others more or less similar are made clear in the light of what St. John of the Cross teaches inThe Dark Night on the night of the senses and that of the spirit. He states that these nights are tunnels through which generous souls, called to a high degree of perfection, to true sanctity, must pass. If a soul emerges from the first tunnel with a heroic degree of the virtues and if, on leaving the second, the heroic quality of its virtues is even more manifest, it is a certain sign that it did not go astray in these very dark and difficult passages, but, on the contrary, gained very great merits therein. These trials are more particularly painful for souls that have a reparatory vocation and that must, in imitation of our Lord, suffer for the salvation of sinners.
In these exceedingly painful dark nights, the soul may occasionally commit a sin, even a serious sin, as happened to the Apostle St. Peter during the dark night of our Savior's passion. But if, like St. Peter, the tried soul rises immediately with deep repentance, it receives a notable increase of grace and charity and it continues its ascent from the very spot where it stumbled for a moment. "Wherefore the penitent sometimes arises to a greater grace," (21) says St. Thomas.
It follows that these obscure periods in the lives of the servants of God, far from being an obstacle to their beatification, on the contrary bring out more clearly the heroic degree of their virtues. Those who have passed through them have triumphed over the most difficult trials which the saints meet with in this life. This is especially true of those who fight more directly against the devil, and who in this way show more clearly the depth of the reign of God in souls that are wholly submissive to Him. Thus are realized occasionally in an extraordinary manner the words of St. Paul: "But the foolish things of the world hath God chosen, that He may confound the wise; and the weak things of the world hath God chosen, that He may confound the strong. And the base things of the world, and the things that are contemptible, hath God chosen, and things that are not, that He might bring to nought things that are." (22)
The article entitled "Possession" in the Dictionnaire theologique catholique states: "In our Western civilizations, men would be inclined to say that the devil is interested instead in dissimulating his action. Does he not hold men so much the better when they ignore or deny him?" (23) But, as Father L. de Grandmaison points out: "In the regions where the Gospel penetrates intensively for the first time, it still encounters, as in ancient times, a sort of occult power, usurped but established, which, by its resistance and manifestations, perfectly recalls the convulsions of the evil spirits in the presence of Jesus. There is hardly a missionary in those countries who has not encountered it." (24)
Why does God permit these diabolical manifestations? St. Bonaventure answers: "It is either for the manifestation of His glory (by constraining the devil, by the mouth of the possessed person, to confess, for example, the divinity of Christ), or for the punishment of sin, or for the correction of the sinner, or for our instruction." (25)
In practice, possession should be admitted only on solid proofs or indications, and the spiritual director should secure the opinion of an experienced physician. St. Philip Neri, although he "thought that persons whom people believe to be possessed by the devil are, in the majority of cases, either sick, melancholy, or mad, nevertheless, judging a certain Catherine, a noble lady of Aversar, to be truly possessed, he freed her from this terrible evil." (26)
On temptation in general and its causes, we advise the reading of the excellent articles by Father Masson, O.P., which were published in La Vie spirituelle, from 1923 to 1926: I. "Temptation in general, its nature, universality, necessity" (1923, p. 108). II. "Its sources: the flesh (ibid., pp. 193, 333); the world (p. 42I); the devil (1924, p. 270; (the tempter, his work, p. 384, his mode of suggestion, by ruse, by violence, his stubbornness; the limits of his power; resistance to temptation)." III. "The processus of temptation" (1926, p. 493). IV. "End of the temptation on the part of the devil, on the part of God: why does God permit temptations? Justice and mercy" (1926, p. 644).