system
Given the following post, respond as if you're commenting on Reddit:
human
What determines if a material melts or burns?

When you apply fire/heat to some materials like ice or plastic they melt, while some metals and coal is set on fire themselves. What determines if a material melts or burns when applied to heat/fire?
gpt
There are two variables: the actual melting point of a material, and the temperature at which the material starts combining with oxygen.

Many materials doesn't combine well with oxygen (like water) so the combustion is small or absent. In that case, they are more likely to melt.

Many others release flammable gases or particles that reacts violently with the oxygen (like wood), or can be directly oxydized (like alcohol). In that case, a combusion is more likely to occur.

In other cases, both can happen: aluminium can melt, but a fine aluminium dust or ribbon is more likely to burn, because of a different ratio between surface exposed to oxygen and volume.