The ghost-story style presented by Henry James in The Turn of the Screw had never been questioned until the publication of the 1934 article by Edmund Wilson titled "The Ambiguity of Henry James".
As it is, this marks the first time that the ghost-story that seems to serve as the foundation to James's novel is seen through a focalized perspective that is completely different from that of a scared governess who fears for the eternal damnation of her charges.
This alternative perspective presents the point of view of a mentally unstable, perhaps hysterical woman, whose impressionable nature gets worsened by the isolation and coldness she gets from living in an old country estate in the middle of nowhere.
The question of the governess's mental state comes as a result of James's consistent use of antithesis throughout the narrative: there is a constant struggle of light versus shadow, fear versus safety, even warmth versus cold.
All of these led Wilson to question whether there is yet another juxtaposition present in the novel in the form of sanity versus insanity. After all, is it not at all possible that a young, impressionable girl placed under the tremendous stress of raising two children on her own in a dark, isolated place slowly begins to lose her mind?
Moreover, James teases the reader by presenting periods of high ghost activity, where the governess is at her highest level of stress; yet, there are also cold periods where the governess does not experience any visions, even when the visions could have been included in parts of the story. Could this be that she was not really seeing anything?
The final answer is that the debate of James's "ghosts" still lives in modern day. Critics are evenly divided, going as far as to comparing the writing trends of James's contemporary ghost-story writers to come to a final conclusion. To this day, the only closure that the argument has received is far from consoling, but is definitely valid: that whether the ghosts of the novel are real or not, it should not take away from the reality of James's carefully crafted ghost-storytelling techniques. In other words, that James has delivered a classic, Gothic, "ghost-story" whether the ghosts in the novel are real or created by the imagination of a psychotic young woman.
Read further on this topic by searching information on Peter G. Beidler's criticism of The Turn of the Screw, as well as Robert L. Gale's on writings of the work. Wherever you choose to research you will find that there is simply not a finite answer; yet, this adds to the multidimensional nature of a simple tale that connects with our schema and our own need for supernatural knowledge in many different ways.