He is as clever as I am.
Is 'As clever as I am' an adverbial clause of comparison functioning as an adverbial adjunct, or is it the subjective complement to the verb 'is'? If the last case is true, what would be its category?
Because I know that in the sentence 'He is clever' clever is an adjective functioning as subjective complement, because the verb 'to be' always takes subjective complement. That's why I think that 'as clever as I am' is a subjective complement, but I read in a grammar book that it is actually an adverbial clause of comparison.
And if it is actually an adverbial clause of comparison, it cannot function as subjective complement, because adverbial clauses always function as adverbial adjunct, so I'm really lost here.