Address & Argument
Invocation
Appealing to a muse, god, or other power for help or inspiration. It can establish the speaker’s dependence on that power or connect the work to a tradition.
"Sing, Heav'nly Muse…" — Paradise Lost
Don't confuse it with Apostrophe. Apostrophe is any address to the absent; invocation specifically petitions for aid at a threshold.
Examples
O Muse, lend me the words to begin this song.
The address specifically asks a muse for help in making the work.
Sing, Heavenly Muse
Milton directly asks the Muse to sing the subject of his poem. It is an invocation and also an apostrophe.
The rest of the family
Rhetorical Question Apostrophe Aphorism Enthymeme Correctio / Epanorthosis Parrhesia Metabasis Amplificatio Aporia Enargeia / Vivid Specificity