system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Why do some objects melt and others catch fire and burn?
gpt
It depends solely on whether the "combustion" reaction for that material needs more energy than the phase change (solid>liquid), or not. If it needs more energy than the object would need to melt, it will melt *first*. If it needs less than object would need to melt, it will burn.

Please note, however, that everything can burn, if heated ~~wrong~~ fast enough. Iron normally would melt, for instance, but can be set on fire nonetheless.