If you have read Henry James's 1898 The Turn of the Screw or seen Jack Clayton's 1961 The Innocents, you know that both depict the belief that certain ghosts exist. Whether or not these ghosts actually exist we do not know. We can only answer the question for ourselves and base our beliefs on the evidence at hand. Though the movie is based on the book, finding a common ground between the two can be difficult.
While reading the book, I found it somewhat difficult to decipher the truth of the existence of the ghosts based on the way the book described the situations. Yes, the governess gave descriptions that were very accurate of Miss Jessel's lover, Peter Quint, and second of Miss Jessel herself. The new governess had never formerly seen her, but she had recently seen a picture of Quint, the lover. The children played very cool, insisting that they knew nothing of the ghosts. Throughout the book, the governess was the only person who ever saw the ghosts that we know of. Yes she provided accurate descriptions and seemed very convincing in her defense. The more I wondered why the ghosts visit and haunt her so obviously, the more I thought that the ghosts were probably real and that the children were dissembling about the ghosts.
Because the viewer can actually see the ghosts in the movie, as played by Peter Wyngarde and Clytie Jessop, that makes it easier to believe that they are real. In the book, when James writes of them, the reader cannot actually see them or the way in which the governess is telling of them. I believe in the movie it is easier to define the plot and see why the ghosts would visit the governess, Miss Giddens (Deborah Kerr). The children, Miles (Martin Stephens) and Flora (Pamela Franklin), act as though they are hiding information, and they change the subject when asked about them or other suspicious matters. Also, physical evidence, such as the supposed teardrop of Miss Jessel in the classroom, makes the existence more believable.
You have to decide for yourself whether you believe the evidence at hand. As for myself, I believe the ghosts were real in both book and movie because they had a purpose for being there. although James makes it harder to believe in them than Clayton does.