In The Bridge of San Luis Rey, the omniscient narrator uses ethos, a form of persuasion based on credibility and authority. After a bridge collapse in Lima kills five people, Brother Juniper decides to study the victims' lives and write a book about them in order to rationally explain why God allowed them to die. The first and last chapters of the book explain the origins and results of this quest, while the middle chapters, which represent the book Brother Juniper writes, tell the victims' stories leading up to the collapse.
All of these chapters are told by the omniscient narrator, who rarely speaks in the first person but claims to know much more about the characters' inner lives than even Brother Juniper can figure out. Outlining the priest's doomed quest to turn the victims' lives into a scientific proof of God's existence, the narrator says that,
[...] for all his diligence Brother Juniper never knew the central passion of Doña María’s life; nor of Uncle Pio’s, not even of Esteban’s.
The reader never finds out who the narrator is or how he possesses so much knowledge that Brother Juniper lacks. But because the narrator speaks so confidently and intimately about the characters' lives, the reader is content to follow along. This authoritative narrative style is an example of ethos.
Through the narrator's insight into the characters' lives, the novel can balance between portraying Brother Juniper's bumbling investigations and actually telling the complex stories he fails to uncover. The narrator's successful use of ethos to draw the reader in and illuminate the characters' lives also draws attention to Brother Juniper's unsuccessful use of logos (appeal to logic) to demonstrate the existence of God, reinforcing the novel's argument that faith can't be articulated or defended on the grounds of logic.
Despite being highly credible, the narrator occasionally questions his own authority. At one point, he muses that although "I [...] claim to know so much more" than Brother Juniper, it's possible that "I have missed the very spring within the spring." In other words, the narrator is saying that the characters' deepest motivations may be hidden even from him. The narrator's questioning of his own credibility prevents the novel from assuming too much authority over its characters. Ultimately, Wilder uses this device to cast doubt on the ability of any work of art to provide a complete portrait of an individual's inner life.
