If you watch the late 80s/early 90s films from Disney, you will see they borrow one great element from musical theater: the use of songs to further plot and/or character development. This is no surprise considering composer Alan Menken and lyricist Howard Ashman both worked doing musicals in Broadway (see: Little Shop of Horrors)
Musicals rely on leitmotifs, an even older musical technique, to identify a specific emotion, idea or character throughout the story. Musical theater takes this to its extreme using not only a musical phrase but a whole song, often with different lyrics, to mark key points in a character's individual story and consequently his or her development. These often carry the word "Reprise" in their title.
In Disney's 1989 film The Little Mermaid, the titular character Ariel dreams of knowing the world of earth-bound humans. Her only contact with this world comes from (presumably) watching ships going by and the odd human artifact that she happens to get by on wrecked ships on the bottom of the ocean. We can see her knowledge is based mostly on her assumptions on what these artifacts do and the (wildly incorrect) teachings of her seagull friend Scuttle.
We see in Ariel a character that is unsatisfied by the status quo and looks forward to getting out of it, a plot that closely resembles Christopher Booker's plot structure called "Voyage and return" in his book "The Seven Basic Plots". In the particular case of Ariel, the desire comes from two main sources:
- The first is her current world/society, where she is the youngest of her father's daughters and thus she's constantly being watched and protected from "the outside world". She feels trapped and used and wishes for freedom.
- The second and most important IMO, is her vision of "the outside world". Her perceived lack of freedom tints her vision and polarizes her ideals, thus seeing her actual world as worse than it is and the other world as better than it is.
This idealized version of the human world becomes patent for us human viewers in her solo piece "Part of your world", where she sings about her views and desires for the society above:
Bet'cha on land they understand
Bet they don't reprimand their daughters
Bright young women sick of swimming
Ready to stand...
SPOILER ALERT
Later in the film, Ariel travels to the surface and sees Prince Eric celebrating his birthday. Ariel gets head over…ahm, fins for him. Then, a violent storm wrecks the ship and she rescues Eric after he falls unconscious to the sea.
When he's safe ashore but still unconscious, Ariel is marveled at having Eric so close and yet so far away from her. At this moment, she starts singing the same tune as before, but this time the lyrics say and mean completely different things:
What would I give to live where you are?
What would I say to stay here beside you?
What would I do to see you smiling at me?
Where would we walk, where would we run if we could stay all day in the sun?
The first time, she wanted to be "Part of that world", still outing herself as a stranger. Now, her focus is on being with Eric and her goal is no longer abstract. It's a smaller and yet a greater thing in her mind.
This, my friends, is character development at its finest. We get to see how Ariel has a similar yet different ambition, made even more clear with the Reprise of her theme. Now, her target has a face and a name and this ambition is what will drive the plot forward:
I don't know when, I don't know how
But I know something's starting right now
Watch and you'll see, someday I'll be
Part of your world