“Good ghosts, speaking by book, make poor subjects, and it was clear that from the first my hovering prowling blighting presences, my pair of abnormal agents, would have to depart altogether from the rules. They would be agents in fact; there would be laid on them the dire duty of causing the situation to reek with the air of Evil. Their desire and their ability to do so, visibly measuring meanwhile their effect, together with their observed and described success – this was exactly my central idea; so that, briefly, I cast my lot with pure romance, the appearances conforming to the true type being so little romantic. This is to say, I recognise again, that Peter Quint and Miss Jessel are not ‘ghosts’ at all, as we now know the ghost, but goblins, elves, imps, demons as loosely constructed as those of the old trials for witchcraft; if not, more pleasingly, fairies of the legendary order, wooing their victims forth to see them dance under the moon.”
Note the absence of the word ‘hallucination’. And a little earlier in this preface to the 1908 New York edition, Henry James reports to have been one of the guests around the fire when the host told the outlines of his story as a hearsay account of a real appearance. At the time a fashionable topic, and Henry James kept himself well informed on the latest developments in the field of scientific measurement of ghosts. And describing the ghosts that haunt Bly, he is in fact defending his choice to ignore their scientific specifications. From which follows that his ghosts originally answered to these specifications. As to be expected from real appearances.