Logic behind ～く form in the negative form of i-adjectives

Question

I'm trying to logically grasp why い-adjectives switch to the ~く form in order to form a negative.

For example:

痛い　　　(is painful)

痛くない　(is not painful)

I understand ない to be an adjective.
い adjectives cannot modify other adjectives. However, い adjectives have an "adverbial" ~く form that can. From that perspective, it seems to be very logical that adjectives assume the ~く form in order to modify ない. (painful-is not)

Though even that's a bit confusing since it feels more natural to me to think of ない as modifying what precedes it...

Am I thinking about this correctly? I'm wondering how this is understood from the Japanese perspective.

Answer 1

Some fun trivia:

• ある is the opposite of ない, but ある is a verb and ない is an adjective. How does that make any sense!? The words like 動詞 (literally "act word") and 形容詞 ("descriptive word") make it sound like words are classified by their meaning, but really they are classified more from the perspective of how they fit the grammar rules, I think.
• When decorating a verb, like 食べない, ない is technically verbal auxiliary. When decorating an adjective, ない is adjective. Both forms of ない have the same meaning and same 活用形.
• Then there's some flavors of ない that's neither and just a part of the word stem, like はかない. In other words, it's adding the negative feel to the whole word, but there's no positive version of the word.

You say it feels more natural to think of ない as a post-decoration of the word before. As a native Japanese perspective, I feel the same way. This seeming complication from the grammar perspective, doesn't match up with how we feel and treat ない. IMO, this is just the rule failing to intuitively describe how we think about the language.

In other words, just another day in messy live language of mankind :-)