It is no secret that song and poetry are close cousins; indeed, song is effectively rhyming poetry that has been put, or was made to fit, music. That being said, poets, novelists, playwrights, singers, and musicians have different names for a reason. No one would call Taylor Swift a poet, for example, anymore than they would call Sir Arthur Conon Doyle a singer.
But are the boundaries between song and literature so firm?
William Shakespeare is called "the Bard" due to his masterful plays which are weddings between stellar stories and sophisticated yet simultaneously evocative wording. A union of skill so great that Early Modern English is also called Shakespearean English. What I am getting at, however, is his title: Bard. In ancient times Celtic bards were poets, musicians, and storytellers whose sacred task was the preservation history, mythology, and genealogies through oral tradition. Bards often served as advisors to kings and chiefs, using their poetry and music to praise or satirize rulers, ensuring their influence in society. Poets, musicians, and storytellers. All three. Alas, the Bardic profession died long ago. Yet some authors keep it alive by writing songs for their books while some musicians and singers do the same by playing those songs or making songs out of time-honored poems.
“There was Eru, the One, who in Arda is called Ilúvatar; and he made first the Ainur, the Holy Ones, that were the offspring of his thought, and they were with him before aught else was made. And he spoke to them, propounding to them themes of music; and they sang before him, and he was glad. But for a long while they sang only each alone, or but few together, while the rest hearkened; for each comprehended only that part of the mind of Ilúvatar from which he came, and in the understanding of their brethren they grew but slowly. Yet ever as they listened they came to deeper understanding, and increased in unison and harmony.” ― J.R.R. Tolkien, The Silmarillion
Any who have read The Hobbit and The Lord of the Rings know that J.R.R. Tolkien designates many pages to song. Whereas other authors typically write something along the lines of "_______ sung a song telling the realm's founder and founding" along with maybe a few lyrics, Tolkien actually writes and includes in full the songs his characters sing. Better yet, he wrote songs in the Elvish language he invented.
Remember that Tolkien was the Rawlinson and Bosworth Professor of Anglo-Saxon and a Fellow of Pembroke College, both at the University of Oxford. Which in regular English means a renowned scholar and professor. One who poured his love, his fascination and delight with and of languages into his legendarium - his songs and languages bringing Middle-earth to life almost as much the story itself.
Thus it is that more modern singers have brought his songs to life, or created ones of their own: such as I See Fire - a song written by Ed Sheeran for end credits of one of The Hobbit movies and, here, performed by the internationally acclaimed Grammy-nominated all-female Irish musical ensemble Celtic Woman.
Where music and literature meet is a harmonious place indeed, and other authors have also created songs and verses for their works, two examples being Anne McCaffrey and Mercedes Lackey.