Consider these adjectives:
The い-declension works for sentence ending as well as directly modifying a noun:
Now if I want to express the adjective as a noun, for example I'm talking about "red(noun)" instead of "a red(adjective) thing":
赤いto obtain the noun
く can be appended to form
赤く which exists as an adverb.
赤になる and 赤くなる are both possible with similar meaning. This leads me to conclude that 赤 is independent from the 赤い which 赤く can be derived from.
But if I try the same thing for 近い I find that I have to add く for it to mean a noun.
Step 1. Remove
近いto obtain the fragment(for lack of a better word)
近does not seem to be able to stand alone (or can it?).
Step 2. Append
But 近く also exists as 近く2 - the adverb that can be derived from 近い.
What is Step 2? It is different from the く-declension for adverbial usage. Why doesn't 赤い get a 赤く noun that is derived from Step 2?