We know that Our Lady is our Mother and that she distributes all the Graces we need, and brings our prayers to Christ. But, she does all this from her throne in Heaven, without us ever seeing her. So, when we hear about Our Lady appearing on earth, what are we to think? Are apparitions possible? If so, what are they?
First off, supernatural apparitions and visions are possible. There are many examples of them in both the Old and New Testaments. Then, there have been many recorded examples throughout the history of the Church – Saint Joan of Arc, for example, had visions of Saint Catherine and Saint Margaret; Don Bosco had visions of Our Lord and Our Lady in the form of dreams.
But, what are they? The answer is: it depends! It depends, because there are different types of visions possible. In fact, there are three main types: corporeal, imaginative and intellectual.
A corporeal vision is the supernatural manifestation of an object to the physical eyes of the body. In some corporeal visions, the figure or object is really present outside of the visionary – either a real body, or else an appearance of a body, made up of rays of light arranged in a certain way. In some other corporeal visions, the object is not really present outside the visionary, but a superior agent (God or an angel, for example) modifies the eye and produces a sensation equivalent to that which an external object would.
Next, we have imaginative visions. In these visions, an image is produced directly in the imagination by a superior agent, or else the agent acts on certain forces calculated to stir up the imagination in a particular way. Finally, there are intellectual visions, where the object is perceived without a sensible image at all.
The problem with all these visions and apparitions is that it can be very difficult to establish whether they are really external, or simply pure products of the imagination. But, even when they turn out to be external, it can be difficult to decide what source exactly they come from. Because, the superior agent which causes them can be good (God, the good angels) or bad (Satan and the other fallen angels).
That is why we must always be wary when we hear about apparitions. Ultimately, only the Church has the authority to decide whether a particular apparition or vision comes from God or not, and this decision of the Church always comes after a lengthy investigation. Any other attitude leaves us open to the possibility of being tricked by the Father of Lies, the Devil.
The apparitions of Our Lady at Lourdes, Fatima, Knock etc. seem to be corporeal visions.