| Public and Private revelation
The various Marian apparitions are classed as "private" revelations, in that the Public revelation of the Church was completed during Apostolic times, and is now closed. All that the Church has done since then is to develop and clarify those public truths, and Catholics are bound to believe them as truths of the Faith.
Private revelations though, including the approved Marian apparitions, are given to an individual or group for their own good or that of others; Catholics are not obliged to believe in them and they do not add to the sum total of Public revelation.
On this point Fr. Frederick Jelly says: "According to Vatican II's Dei Verbum, the Magisterium of the Church has the charism of infallibility only when Scripture and Tradition, in mutual interdependence, form the foundation for a dogma - whether solemnly defined by an ecumenical council, by an ex cathedra pronouncement of the Pope, or by the universal ordinary Magisterium, that is the constant preaching and teaching (sensus fidelium) of the Church as a whole. The certitude that can be reached as a result of investigating apparitions and private revelations can never be the certitude of divine faith ..."
There is always the danger of illusion or deception in visions or apparitions, and that is why the Church, in the person of the local bishop initially, has always been reluctant to accept them without a great deal of scrutiny. In approving particular private revelations the Church is only proposing them for assent on the basis that they require an act of human faith based on human testimony.
The classic view on this matter was expressed by Pope Benedict XIV (1675-1758), as follows: "Although an assent of Catholic faith may not and can not be given to revelations thus approved, still, an assent of human faith, made according to the rules of prudence is due them; for, according to these rules such revelations are probable and worthy of pious credence."
Marian apparitions as a "special" form of private revelation
It might be remarked in passing though that Pope Benedict wrote in the period before the major modern Marian apparitions, and so obviously did not say the last word on the subject. This is particularly so if we recognise the special nature of the messages received and transmitted by the various more recent Marian seers, which seem to go beyond "private" revelation. At the very least they seem to be a special case of such revelation, since they form a series which has been of great importance in strengthening the Church in modern times.
They certainly differ from the various "private" revelations given to individual saints which might have been concerned with, for example, the foundation of a religious order. That is such revelations only concern part of the Church, whereas the major Marian apparitions have been taken up by the Church as a whole, and so can, in some sense, be described as "public."
As Fr. William Most states, "Some private revelations of our own times, such as those at Fatima, are directed to all Christians, not only to one individual; still they are technically called private, to distinguish them from that revelation which closed with the death of St. John."
Thus we have to distinguish between those revelations made to individuals, for their own good, and those meant for the whole Church. Fatima and Lourdes certainly fall into the latter category, and, given the miraculous events surrounding them, which are evidence of the divine, seem to call for more than a simply "human" faith, even if it does not appear that they demand a truly "theological" faith.
The fact that these apparitions seem, from a secular historical point of view, to have been of little importance, is not the crucial point; the same could be said for Israel, which too made little impression on history, and yet our whole civilisation is built on the foundation laid by that small country.
In the same way the Marian apparitions have a significance that goes far beyond their surface importance as a reiteration of the Gospel message of prayer and repentance. They can also be seen as the first presentiments of the certain fact that Christ will come again at the Last Day. Mary was an intimate part of Christ's first coming, and similarly, she has an important role in preparing the way for his second advent, principally, it would seem, by means of her apparitions.
Stages in Church approval of apparitions
The decision as to the authenticity of particular apparitions rests in the first place with the local bishop, who is the "Pope" of his own diocese. If after sufficient study there is solid evidence to support the apparition, in terms of the facts surrounding it and the activities of the seer or seers, and also regarding such matters as miraculous healings, then the bishop is empowered to issue some form of edict declaring the authenticity of a particular apparition.
Such a statement is not of course infallible, and no one is absolutely obliged to believe in that particular apparition, but the position of the bishop as the spiritual leader of the diocese means that his decision should be respected, and certainly not treated dismissively. Over time the papacy may grant special privileges to particular shrines, and these are a sign of further approval by the Church as a whole.
One such liturgical sign is the granting of a feast day, as for example that of Our Lady of Lourdes on 11 February. In recent times popes such as Paul VI and John Paul II have visited a number of Marian shrines, thus giving them the highest possible level of approval. These are the elements then that we have to bear in mind when considering the authenticity of the Marian apparitions of the nineteenth and twentieth centuries.
For details about St. John of the Cross and St. Teresa of Avila on visions and visionaries click here
Sources: Rev. Michael Walsh, The Apparition at Knock, (St Jarlath's College, Tuam, 1959); Fr. Frederick M. Jelly, OP, "Discerning the Miraculous: Norms for Judging Apparitions and Private Revelations," in Marian Studies 44, 1993; Fr William Most, Mary in our Life, (The Mercier Press, Cork, 1955); Joseph de Sainte-Marie, OCD, Reflections on the Act of Consecration at Fatima of Pope John Paul II on 13th May 1982, (Augustine, Devon, 1983); Louis Lochet, Apparitions of Our Lady, Their Place in the life of the Church, (Herder, Freiburg, 1960).