There is an implicit narrator in all narrative writing, which includes chronicling, historical writing, and almost all novels. This is by contrast with performance literature, such as drama and film, where the use of a narrator is generally considered to be a sign of poor writing.
One of the first things anyone learns when studying literature, or starting to write, is that narrators are generally first person ‘I’ narrators or third person ‘then he did’ narrators. Occasionally — although it makes for tedious reading — you encounter a second person ‘you’ narrator (do you see what I did there?). A section of the Biblical book of Acts is written as a first person plural ‘we’ narrative.
Two other distinctions are between the limited and the omniscient narrator, and the reliable and the unreliable narrator. Actually, this is more of a continuüm than a distinction. Generally speaking, the limited narrator is the characteristic voice of factual chronicling, and the omniscient narrator is the dominant voice of fiction, while the unreliable narrator is the dominant voice of the historian. But, as literature has become more sophisticated, all of these voices are now fairly common in fiction.
Here are some classical examples:
Limited narrator: Plato — Protagoras. With all of Plato’s writing on Socrates, he writes from the point of view of a listener, without insight into the actual thoughts of Socrates or his listeners
Omniscient narrator: Homer — Odyssey. Homer freely skips around the Greek world, taking us to conversations which are held in the supernatural world
Unreliable narrator: Herodotus — Histories. Herodotus recounts information which has been provided to him, but occasionally points out that he himself does not believe a particular story. In this way, he invites the reader to doubt the narration.
We need to draw a sharp distinction between an unreliable narrator as a distinct narratorial voice, and a narrator we happen to disbelieve. For example, as historians, Tacitus, Eusebius and Pliny all include passages which cause us to doubt their veracity. But they are not writing as unreliable narrators as such.
The advantage of the omniscient narrator is that it exactly reflects the true state of the the fiction author. If you are the writer, then you know exactly what has happened, what will happen, and the entire state of all relevant information in your world. You are free to introduce whatever information you like at whatever point, or to hold it back, and you can make the reader privy to the thoughts of any or all of your characters.
The disadvantage of the omniscient narrator is that it is intrinsically less realistic than a limited narrator. If you are trying to create the impression that ‘all this really happened’, then use of narrator omniscience breaks the illusion.
Almost any ‘I’ narrative will involve a limited narrator, but as soon as you introduce an ‘I’ narrative, you create an interesting possibility. Supposing the narrator, who is also an actor in the story, has not fully understood what is going on? Jonathan Swift uses the naïve narrator to great effect in Gulliver’s Travels, and also, as recently discussed on ‘In our time‘, in ‘A modest proposal’. The naïve narrator is an ideal tool for the satirist, creating rich ironies of the kind that satirists love. A naïve narrator can be pompous, stupid, misinformed, or anything you like. Although Swift made this tool his own, it first appears in English in the works of Geoffrey Chaucer, where he introduces himself as a person unable to sleep in The Book of the Duchess. But Chaucer develops this notion further in the Canterbury Tales, where he introduces his narrator as not only naïve, but, frequently, simply incompetent or misinformed. Like Herodotus, he makes it clear that he is inviting us to doubt him, but, unlike Herodotus, he wants us to doubt not his information, but his judgement. Chaucer uses this for comic, ironic effect. Later authors use it for enhanced realism, to confuse the unwitting reader, or to create deliberate ambiguities so that a book can be read in contradictory fashion on different levels. By the time we reach modernism, we even have the spectre of the unreliable author, raised by William Golding in his collection of essays The Hot Gates where he suggests that the author’s interpretation and intention are no more reliable than those of the reader.
Golding is probably the most interesting exponent of the unreliable narrator. In Lord of the Flies, he tells the story ‘straight’, as a limited third person narrator. But, by the time we reach Pincher Martin, we have a story which is told almost entirely ‘incorrectly’, leaving the reader to grasp, at their own speed, what is ‘really’ going on. In many ways, Pincher Martin is a story which is only worth telling in the way that Golding tells it. But, in The Spire, where Dean Jocelin’s story is told in a third-person stream of consciousness, there is a real question about whether the story is actually worth telling at all, and whether the hopelessly confused and misled narrator does anything more than confuse a story which, once understood, is relatively unremarkable. That’s a critical judgement which I won’t go into at this point. Be that as it may, when he wrote his later work Darkness Visible, Golding returned to an omniscient narrator voice.
What to do with narrators? If you’re a reader, it’s probably worth accepting that any ‘I’ narrative written after Chaucer is at the very least done in this way with the possibility of the narrator being a naïve narrator. The more sophisticated the writing, the more chance that they are actually telling the story in a way which is at odds with how the author sees the story ‘really’ unfolding.
If you’re a writer, it’s worth thinking twice before jumping straight in with unreliable narration. In the days of post-structuralism and deconstruction, whatever you wrote was liable to be treated as unreliable whether you wanted it that way or not. But most readers are not literature graduates, and even most literature graduates did not study in the heyday of deconstruction. If you adopt a needlessly complex narration system, you run the risk of your readers not understanding what you are doing, missing the point, and ceasing to read: at this point, your book has failed the one test it needs to pass. If you have a compelling reason for an unreliable narrator, then you need to include sufficient clues for the reader to understand this, and to follow the story as you go.
My opinion: far too many of the books I have read recently have needlessly complicated narratorial structures, with mixtures of frame-narratives, I-narratives, he-narratives, even you-narratives, and combinations of reliable and unreliable narrators, all juxtaposed in such a way that the reader has to solve a puzzle just to grasp the story. There are actually very established ways of introducing unreliable narration without confusing the storyline. These include dialogue, documents (such as letters), and storytelling within the story.