Ballad Characteristics:
* Slow Tempo: "Jar of Hearts" is definitely slow and has a melancholic feel. Check.
* Emotional Content: It deals with heartbreak and loss, a common ballad theme. Check.
* Simple Structure: Ballads often have a simple structure with a clear verse-chorus pattern. "Jar of Hearts" fits this pattern. Check.
* Focus on Story: While the lyrics are emotionally driven, they do tell a story of heartbreak and betrayal. Check.
Where it Deviates:
* Instrumentation: While the song uses piano and strings, it also features drums and a more modern, pop-influenced sound. This makes it less traditional than a purely acoustic ballad.
Conclusion:
"Jar of Hearts" is a ballad with a modern twist. It incorporates the core elements of a ballad (slow tempo, emotional content, simple structure, storytelling), but it also has a more contemporary sound and instrumentation. Ultimately, the classification depends on your personal definition of a ballad.