The first line of this book tells us we're dealing with a third-person narrator:
If I am out of my mind, it's all right with me, thought Moses Herzog. (1.1)
Holy omniscience, Batman. We know from the get-go that this narrator has some serious mind-reading abilities. But we need to read farther on before we realize that this narrator's omniscience is limited completely to the mind of Moses Herzog. And the mind of Moses Herzog is limited completely to thinking about… the mind of Moses Herzog. Claustrophobic yet?
To make this book (hey, it's called Herzog) even more Moses-centric, we spend so much time reading Moses' letters that it's as if much of this story is told by Herzog in the first-person. Still though, the outside narrator is always there keeping an eye on things—and keeping us from getting cabin fever inside Moses' skull. If this book teaches us anything, it's that living 24/7 in Herzog's mind is worse than solitary confinement.