The speaker addresses someone absent or dead, a thing, a place, or an idea, as if they could hear.
In the Odyssey
tell me, Muse, of the man of many turns, who wandered far after sacking the sacred citadel of Troy.
The narrator addresses the Muse as if she were present and could hear him: "tell me, Muse." The invocation places the song under the authority of a goddess and already announces the subject of the poem, the man of many turns.
Book I: The council of the gods and Telemachus, the narrator
ah, Father Zeus, Athena, and Apollo! Would that you, being such as you are, thinking what I think, had my daughter and were called my son-in-law, staying here; I would give you a house and goods, if you stayed willingly; no one of the Phaeacians will hold you against your will; may this not be dear to Father Zeus.
Book VII: The palace of Alcinous, Alcinous
endure, heart! You have endured something even more vile, on the day the Cyclops, of irresistible strength, devoured my brave companions; you endured, until my plan drew you out of the cave, when you thought you would die.
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