In the book The Japanese Copula: Forms and Functions there's a passage that says:
The existence of an adverbial copula is expected when we consider the fact that adjectives inflect to end form, the pre-norminal form and the adverbial form without the help of the copula ar-
Trying to wrap my head around what is an adverbial copula, I realized the following:
In Japanese, you can move a verb to before a noun to create a subordinate adjectival clause.
castle SUB to move 城 が 動く The castle moves. to move castle 動く 城 A castle that moves. A moving castle.
A copula is a verb, so you can do the same with it, except that な is the adjectival version and だ is predicative.
country SUB peaceful COP 国 が 平和 だ The country is peaceful. peaceful COP country 平和 な 国 The country that is peaceful. A peaceful country.
So does this mean that every na-adjective in Japanese technically introduces a new clause? Because な is a copula. A copula is a verb. You can't have two verbs in a single clause. So every time there's a な there must be a new clause, right?
COP-ADV 平和 に 生きる To live peacefully.
If に is an adverbial copula, that means 平和に is a subordinate adverbial clause?