The Turn of the Screw: Metaphor Analysis

Ghosts as a metaphor for evil in people
At first, it seems the governess is just concerned with the actual, physical presence of the ghosts. However, as the novel progresses, she is clearly increasingly concerned that the ghosts represent evil in the children. She tells Mrs. Grose that the ghosts want to get to the children "For the love of all the evil that, in those dreadful days, the pair put into them. And to ply them with that evil still, to keep up the work of demons, is what brings the others back" (64). She is convinced that their contact with Miss Jessel and Quint has made them evil, and that their continued interaction with their ghosts makes them more evil still.
Because the children choose to interact with the evil ghosts and not tell her about it, the governess assumes they are also evil. She proclaims that Miss Jessel wants the children to join in "the torments . . . of the lost" (78) and that Miles is wicked because he was so long in the company of Quint (79). When, at the end, Miles is looking for the ghost he knows she thinks is there, she challenges him to name the ghost. When he does, she assumes she has won a victory over evil because he is choosing to tell her about the ghost instead of hiding and protecting Quint. "I have you," she tells him, "but he has lost you for ever!" (113). In her view of things, Miles has chosen good over the damned and the wicked and so has been saved.
Despite the governess's interpretation, the ghosts could also be construed as evidence of her own evil thoughts. The fact that she could even imagine there are ghosts roaming the halls means her own mind is impure. Miles clearly sees things this way. When he names the ghost at the end, he says "Peter Quint-you devil!" (113). The governess chooses to interpret this as a condemnation of Quint, but it is more reasonable to assume he is calling her a devil. She, herself, admits to having an "infernal imagination" (66), the only kind of imagination that could come up with ghosts. Moreover, she clearly fabricates a conversation with Miss Jessel to tell Mrs. Grose about. This indicates that her own evil thoughts are actually creating the ghosts.
Either way, ghosts are physical manifestations of the evil within minds. Whether the governess or the children are the ones with evil thoughts, the ghosts themselves are a consistent symbol of evil.
Theater
Watching and being watched are continually recurring images in this book. The governess talks of seeing ghosts from afar, she sees Quint through a window and then Mrs. Grose sees her through the same window, and she fantasizes about viewing the master as she comes around a bend. In one scene, she and Mrs. Grose sit watching the children walk the grounds and read. She puts her own interpretation on the scene, explaining that they are talking about the ghosts (63). All this viewing is reminiscent of people at a play who interpret the scene in front of them.
In the theater, the actors look out and see nothing, but the people in the audience see the actors clearly. Sometimes, this is also the case in Turn of the Screw. When Miles sneaks out at night, he is putting on a show for the governess. She looks because there is another audience member, Flora, so she is compelled to also view. When she sees him, he is looking at Flora in the window above. So, the children are putting on a show that consists of watching one another, and the governess is the audience for this show.
James underscores the theatrical nature of this text with numerous references to the theater. When she describes Quint, the governess says he seems like an actor (32). Actors were disreputable, lower class people, but they were often dashing and handsome. The romantic life they led was not respectable but was nonetheless appealing and fascinating to respectable people. When James makes reference to the theater, he is pointing out how tantalizing it is to watch others and to fantasize about the evil in their lives. He had himself recently met with a humiliating failure in the theater, and so when he compares something to the theater, he is being insulting.
James thought contemporary theater was melodramatic and unrealistic, much like the governess. He makes many references not just to watching but to the theater in particular to underscore the way she is being melodramatic. The governess compares Bly to "a theatre after the performance-all strewn with crumpled playbills" (67). The place where her drama is played out is indeed a theater, and she later acknowledges that she is inventing a drama when she explains that "the curtain rose on the last act of my dreadful drama and the catastrophe was precipitated" (71).
These are a few of many references to the theater and plays. James compares the governess to a theater professional who lets his or her own sense of the overly dramatic take away all sense of reality.