At the beginning of Chapter 6, the narrator interjects to apologize for the mundane events of the novel so far. It is an early hint at the narrator's playful role in telling Thackeray's story—and the possibility that the narrator might not be entirely reliable:
I know that the tune I am piping is a very mild one, (although there are some terrific chapters coming presently) and must beg the good-natured reader to remember, that we are only discoursing at present, about a stock-broker’s family in Russell-square, who are taking walks, or luncheon, or dinner, or talking and making love as people do in common life, and without a single passionate and wonderful incident to mark the progress of their loves.
In this passage, the narrator essentially admits that they can't wait to change the subject—they hint to the reader that there is excitement around the corner—and they acknowledge that the Sedley's, whom they have been discussing so far, haven't had a "single [...] wonderful incident" yet. This aside therefore serves to remind the reader that the narrator has a very clear idea of what's going to be happening over the course of the novel, but they're only willing to let the reader in on the drama a bit at a time.
Although this passage does not show the narrator at his most duplicitous, it is an important reminder that the reader should look elsewhere if they are hoping for a straightforward exploration of upper-class life in England. Thackeray's novel is a work of unrelenting satire, and such a work requires a partisan narrator who is just as prepared to cast judgement on the characters and their behavior as readers themselves are.
In Chapter 25, the narrator continues to whisk the reader around the interlocking stories of Vanity Fair somewhat out of order, and this ultimately maximizes each story's dramatic effect. The narrator uses a lengthy and somewhat convoluted simile to emphasize his privilege in knowing the bigger picture and delivering it to the reader in the best possible fashion:
As you behold in Her Majesty’s drawing-room, the ambassadors’ and high dignitaries’ carriages whisk off from a private door, while Captain Jones’s ladies are waiting for their fly: as you see in the Secretary of the Treasury’s antechamber, a half-dozen of petitioners waiting patiently for their audience, and called out one by one, when suddenly an Irish member or some eminent personage enters the apartment, and instantly walks in to Mr Under-Secretary over the heads of all the people present: so, in the conduct of a tale, the romancer is obliged to exercise this most partial sort of justice.
Just like various important people have the authority to bypass the general public in order to discuss important matters with other important people, the narrator has the authority to move around the story and bypass certain events to keep the reader engaged. "Our history," the narrator offers earlier in this same aside, "is destined in this Chapter to go backwards and forwards in a very irresolute manner"—and the narrator believes "we have occasion to step back to yesterday, so that the whole of the tale may get a hearing."
This is one of countless examples of the narrator's unreliability in Vanity Fair—he'll tell the reader a compelling story, to be sure, but it might not be the most straightforward one, and he might not tell it the way it actually happened.
At the beginning of Chapter 50, the narrator shifts his attention away from Lord Steyne and the entertainment of the upper class in order to bring the reader up to date on the Sedley family, who is living in poverty. To make this shift, the narrator makes an allusion to the narrative practices of classical poetry:
The Muse, whoever she be, who presides over this Comic History, must now descend from the genteel heights in which she has been soaring, and have the goodness to drop down upon the lowly roof of John Sedley at Brompton, and describe what events are taking place there. Here, too, in this humble tenement, live care, and distrust, and dismay.
The muses are a time-honored device of Greek literature. Ancient Greek poetry, particularly epic poems, traditionally begin with an invocation to the muses not dissimilar from the narrator's playful invocation in this passage: according to Greek mythology, the muses are the goddesses of creative inspiration for everything from music to astronomy. By praying to the muses at the beginning of a work of literature, authors could ensure their work's quality would reflect such divine inspiration.
Throughout Vanity Fair, the degree to which the narrator has control over the story remains unclear. At some moments, the narrator whisks the reader from vignette to vignette according to his whims, but in other moments, like the one above, he defers to the powers that be—the forces of literary convention. In this case, Thackeray is having a bit of fun with the constraints of this convention and the unreliable narrator as a literary device. The reader is already familiar with how wealth and vanity fascinate the narrator: while he would prefer to continue soaring amongst the heights of English society, the Muse (which is to say, Thackeray) drags him—and the reader—back down to earth.
In Chapter 64, Thackeray—or the narrator—compliments himself on his careful portrayal of Becky's behavior and further establishes the unreliability of Vanity Fair's narration. The narrator also makes an allusion to the mythical siren in order to better characterize Becky's deadly charisma:
I defy any one to say that our Becky, who has certainly some vices, has not been presented to the public in a perfectly genteel and inoffensive manner. In describing this siren, singing and smiling, coaxing and cajoling, the author, with modest pride, asks his readers all round, has he once forgotten the laws of politeness, and showed the monster’s hideous tail above water? No! Those who like may peep down under waves that are pretty transparent, and see it writhing and twirling, diabolically hideous and slimy, flapping amongst bones, or curling round corpses;
In Greek myth, the siren is a monster with the appearance of a beautiful woman who lures sailors into the water to kill them. By describing Becky as a siren, the narrator is also congratulating himself for disguising her worst qualities so effectively. It is only now that he reveals her true monstrosity.
In addition to confirming the narrator's untrustworthiness—has he been toying with the reader?—this passage produces another powerful, gendered image of Becky's character. The trope of feminine beauty disguising monstrosity is present throughout literature, from Ancient Greece through to today, and connects to a longstanding stereotype of female characters as inherently, or inevitably, deceitful.
