Can you explain the narrative techniques in The Turn of The Screw?

The governess is what we would call an unreliable narrator. She is unreliable for a variety of reasons- the most popular reason amongst critics being that she is insane. Following the psychological analysis of the governess' insanity, one can argue that the ghosts are not real, but figments of the governess' imagination- this would make her accounts of the ghosts unreliable. 

Upon close analysis of the text, we see that all opinions we get from the other characters are written by the governess herself, for example when Mrs Grose says 'May I-' the governess interrupts with 'Kiss me?'. There is no evidence to suggest that this is what Mrs. Grose was really going to say. The fact that all opinions of the characters are articulated from the governess makes her an unreliable narrator, as she could be incorrectly portraying the characters and their views.

It is important also to recognise there are different types of unreliable narrators- such as 'fallible' and 'untrustworthy'. A fallible narrator is when the narrator believes she is telling us the truth, but is not due to incapabilities such as telling the story years after, or believing something to be true which is in fact not. However an untrustowrthy narrator purposefully misleads the reader, so the governess claiming Flora saw Miss Jessel is a way to justify her aggressive outburst towards her.

An argument I delved into during my studies of detective fiction in university was to place the governess as an untrustworthy narrator due to being a suspect in the murder of Miles- and the purpose of her manuscript to be one that feigns insanity in order to excuse herself for the murder.