Epistolary
Epistolary writing presents the work as a letter, addressed to a named recipient who never replies. The word comes from the Latin epistula, meaning letter, and the form has a long life in fiction, from eighteenth century novels told entirely in correspondence to modern narrators writing to a silent friend. In a song it shows in a direct salutation, a second-person addressee held throughout rather than glanced at, and the sense that the listener is reading something not written for them.
The letter frame gives the speaker a reason to explain herself at length and licence to be blunt, since a letter is private even once it is published. It also creates two audiences at once: the person addressed, and everyone else who overhears. That double address is where the sense of accountability comes from, because the writer sets out what changed and how while the recipient gets no chance to answer. Distinct from apostrophe, which is a single moment of address rather than a sustained frame, and from dramatic monologue, which holds a silent listener without needing a letter to do it.
Appears in 1 song
“Dear John, I see it all now that you're gone”
Uncle Jerry opens his reading of the poem by naming the frame: this is a letter, and the salutation is the signal. He gives the Latin root, epistula, and sets the song against the tradition of novels told in letters, noting Austen inserting letters to move a narrative along and Ring Lardner's baseball pitcher writing home to his friend Al. He argues the form does specific work here. It gives the narrator a reason to explain how she changed through an experience, it creates a reading public as well as an addressee, and it lets her supply the other person's side of the exchange without him ever answering. His closing verdict is that the song is a dramatic monologue delivered through an epistolary frame.
The letter frame is the poem's premise rather than a flourish. It explains the direct address, the licence to be blunt, the sense of a private document made public, and the fact that the accused never gets to reply.