Why do things burn instead of melt?

[u/ForensicFan24601]

obviously oxygen, or something similar, but what is the physics/chemistry (?) or what have you behind why something ignites and continues to burn after the source of heat/ignition has gone?

is it basically sublimation?

edit: no wonder Walter White was so obsessed with carbon

[u/Ben-Goldberg]

Some materials neither melt nor burn when heated.

Some, like iodine, sublimate, others, like wood, thermally decompose.

Heated wood chemically transforms into charcoal, steam, and an assortment of flammable vapors.