The great number of authors who have written upon the apparitions of angels, demons, and disembodied souls is not unknown to me; and I do not presume sufficiently on my own capacity to believe that I shall succeed better in it than they have done, and that I shall enhance their knowledge and their discoveries. I am perfectly sensible that I expose myself to criticism, and perhaps to the mockery of many readers, who regard this matter as done with, and decried in the minds of philosophers, learned men, and many theologians. I must not reckon either on the approbation of the people, whose want of discernment prevents their being competent judges of this same. My aim is not to foment superstition, nor to feed the vain curiosity of visionaries, and those who believe without examination everything that is related to them as soon as they find therein anything marvelous and supernatural. I write only for reasonable and unprejudiced minds, which examine things seriously and coolly; I speak only for those who assent even to known truth but after mature reflection, who know how to doubt of what is uncertain, to suspend their judgment on what is doubtful, and to deny what is manifestly false. As for pretended freethinkers, who reject everything to distinguish themselves, and to place themselves above the common herd, I leave them in their elevated sphere; they will think of this work as they may consider proper, and as it is not calculated for them, apparently they will not take the trouble to read it. I undertook it for my own information, and to form to myself a just idea of all that is said on the apparitions of angels, of the demon, and of disembodied souls. I wished to see how far that matter was certain or uncertain, true or false, known or unknown, clear or obscure. In this great number of facts which I have collected I have endeavored to make a choice, and not to heap together too great a multitude of them, for fear that in the too numerous examples the doubtful might not harm the certain, and in wishing to prove too much I might prove absolutely nothing. There will, even amongst those I have cited, be found some which will not easily be credited by many readers, and I allow them to regard them as not related. I beg those readers, nevertheless, to discern justly amongst these facts and instances; after which they can with me form their opinion--affirm, deny, or remain in doubt.