The key idea of the theory is that poets have a store of formulas (a formula being ‘an expression that is regularly used, under the same metrical conditions, to express a particular essential idea’)[1] and that by linking the formulas in conventionalised ways, poets can rapidly compose verse.
Source: Oral-formulaic composition – Wikipedia
Tim B.
https://en.wikipedia.org/wiki/Albert_Lord
“Lord demonstrated the ways in which various great ancient epics from Europe and Asia were heirs to a tradition not only of oral performance, but of oral composition. He argued strongly for a complete divide between the non-literate authors of the Homeric epics and the scribes who later wrote them down, positing that the texts that have been preserved are a transcription by a listener of a single telling of the story. The story itself has no definitive text, but consists of innumerable variants, each improvised by the teller in the act of telling the tale from a mental stockpile of verbal formulas, thematic constructs, and narrative incidents. This improvisation is for the most part unconscious; epic tellers believe that they are faithfully recounting the story as it was handed down to them, even though the actual text of their tellings will differ substantially from day to day and from teller to teller. “