system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do things catch fire without flame I.e just from heat?

My wife is adamant that things can’t catch fire without flame. I know you can burn them with just heat, but can’t really explain why. Save our marriage!
gpt
>How do things catch fire without flame I.e just from heat?

The only reason a flame can set other things on fire is because of the heat it generates.  So the reality is that the **only** way to catch things on fire (ignoring unusual chemical reactions) is from heat, and other flames just happen to be one way to provide the necessary heat.

Also, ask your wife how you can light a match by striking it on a matchbook if it takes a flame to set things on fire.