"light a fire"

Why do we talk about lighting a fire? After all, if there is already a fire, there's no need to light.

I don't understand the question. Please, elaborate.

If you light a candle, you set it on fire. However, there be no point in lighting a fire, as there already is fire. No one really lights fire as it's already there.

Where is the fire (before lighting a fire)?

because a "fire" is more than just the actual flame, or Fire in its generic sense. It can also mean a setting, like a bonfire, in which case you would have to light.

If you take a lit match and put it up to a candle, then you're lighting a candle, if you take a lit match and put it up to a lit campfire then you're lighting a fire. There's no point in doing the latter, as there already is fire there.

I'm still in a dark.
Seriously, I don't understand what do you want. How would you say "light a fire"?

<<I'm still in a dark.
Seriously, I don't understand what do you want. How would you say "light a fire"?>>

You "start a fire".

<<You don't put it at a lit campfire; you put the match on a pile of wood to start it burning.>>

Yeah exactly. A pile of wood is not a fire, hence you're not actually lighting a fire.

<<I'm still in a dark.>>

Was there a pun intended there?

In other words, when you light something, you set it on fire. If you lit a trash can, you'd set the trash can on fire. You can't set fire itself on fire. The question is then, why do we say "light a fire" as a synonym for "start a fire"?

<<I'm still in a dark>>
No pun, just playing with words.

OK, why do we say light a candle and not start a fire on a candle?

Or better; set a candle on fire?