lime_glowwormWhat causes flames to exist
It’s another state of matter. You know gas, liquid, solid, right? Well, there’s actually a shitload of those, not just three. The fourth they’ll teach is called plasma, and it’s when the atom has gotten busted up into floating electrons and nuclei. Your candle flame is a plasma.
The light from a lightning bolt is from glowing plasma too. So is the surface of the sun for that matter.
Only very hot flames are a plasma and usually only within certain regions of the main body of the flame; most flames one encounters in their life will not be a plasma due to low or non-existent ionization. A candle flame is almost certainly not a plasma, rather it's a combusting (oxidizing) gas which appears as a flame due to the emission of photons in the visible range from regions where the fuel is reacting with air.
I’ve read that most visible flames in campfires are just glowing soot