What I mean by this is, take waterbanders for example, they need water to bend this is an external source for their bending. An example of an internal source would be firebending since it comes from their chi. So do Airbenders rely on an external source because there is air in the world or does it come from inside them like firebening.
well, past Xpert, upon further examination of the show, the bender that relies on external elements (watebenders and earthbenders) have to pick up said element while firebenders don't have to do that
Firebending is like this becuse it comes from the user. Air is the same way. Take this picture of aang for example:
He is firing a gust of air the same way a firebender (except they might use a fist instead of a palm) would. Hence the airbenders rely on and internal source to bend the element of air.
Also, This very helpful comment by Xalbek: youtu.be/xvY_C0CmgSY?t=9 | Mako bending fire he didn't create youtu.be/plBliszsArA?t=162 | Iroh bending surrounding fire with breath youtu.be/fBFiITicPBQ?t=43 | Jeong Jeong bending the fire from candles These scenes combined with the description from: (avatar.fandom.com/wiki/Firebending) leads me to interpret that while Firebenders can bend existing fire, it isn't as useful as generating their own – Xalbek