Writing A Piano Ballade

Wondering what the form is of most piano ballades.. I understand its a variation of Sonata form, but in what way ? what makes a solo piano instrumental, a "Ballade." When I say piano Ballades, I'm mostly referring to those of Chopin; the "original" solo piano ballades.. But also newer ballades as well.

Thanks everyone !

Chopin, according to Robert Schumann, apparently based the ballades off of specific poems. This would be why Chopin chose to name them the literary title of "ballade". As far as form is concerned each one is different. My favorite is his fourth ballade, the form is a combination of sonata and variation form. I liked the form so much, it greatly influenced how I composed my Sonata-Fantasie for piano (which you can check out on this forum I might add :thumbsup:).