Three main themes of The Turn of the Screw are the struggle between good and evil, the difference between reality and fantasy, and the existence of supernatural spirits. By leaving many issues unresolved at the end of the novel, Henry James encourages the reader to reach their own conclusions about how these themes affect the characters.
Good and evil are apparently represented by the young, innocent children as contrasted to the malevolent, deceased Quint. The governess is determined to protect her charges, Miles and Flora, from evil forces. As the novel progresses, however, it appears that she may have arrived too late. The reader then begins to wonder if the evil represented by Quint and Miss Jessel—the late, former governess—has already infected the children, or even if Miles had a hand in their deaths.
Because the novel is told from the governess’s perspective, the reader cannot learn if her version of events is accurate. She may be imagining the things that seem to be occurring around her. As she herself increasingly doubts what her senses convey to her, the reader also wonders if she is in the throes of a mental breakdown.
The impact of her possible fantasy, imagination, or hallucination raises significant questions. Are Quint and Miss Jessel hovering around the estate as ghosts? If so, is there something about the circumstances of their deaths that are negatively affecting the children? The governess’s doubts and possible mental lapses are thus associated with the theme of belief in supernatural forces.