Where does the な used in な-adjectives come from? -adjectives are derived from nouns. This is similar to how can be used to 'Adjective-ize' a noun. But while it's clear how -adjectives work, and why the is appended, what is the story for -adjectives? How are they derived? Why is the appended?

_(I was surprised to see that I cannot find another thread that discusses this. Perhaps my search-fu is weak...)_

The used for adjectives has a clear historical derivation. This started as , the adverbial particle, + , the classical terminal (sentence-ending) form of modern . + then contracted to for the terminal form. If a adjective came at the end of a sentence, in classical Japanese, it would end with , as in You might still encounter this form from time to time in poetry.

Classical terminal had an attributive form (when modifying another noun) of . So + contracted to , as in . Again, this form still appears in poetry, especially if the author is trying to evoke an old-fashioned or traditional feel.

As time passed, the terminal form disappeared, replaced with the modern , and the attributive form contracted even further into just .