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.