I understand the
的from the structure:
Adj + 的
as attaching the
Adjto an omitted Noun. This omitted Noun can either be a general noun such as "one/s" (高的 can mean the tall one) or an implied Noun from the context (if the topic is a boy, 高的 could mean a tall boy).
I have come across the following structure for reduplication of adjectives:
Noun + Adj + Adj + 的.
His son is tall.
Adj + Adj + 的 is attached to an omitted noun, it becomes a nominal phrase and grammatically
Noun + Adj + Adj + 的 is equal to
Noun + Nominal Phrase. Where is the verb and predicate in this sentence? Is the verb copula 是 omitted but implied in connecting the nouns：
Noun +（是）+ Adj + Adj + 的？From the example: 他的儿子（是）高高的？
Edit: My original post addressed the question focusing on the function of 的. However, the question of why 的 was necessary in reduplication of adjectives, instead of
(Adv of degree) + Adj + Adj, was already asked in Adverbs of degree with reduplicated adjective phrases?