What kind of phrase/clause is "as far as I know"?

Question

I would like to know what kind of phrase/clause "as far as I know" is, and why.

Answer 1

"As far as I know" is an adverbial clause. Like an adverb, the phrase modifies another verb/adverb/adjective, in this case another verb. For example, in the sentence "As far as I know, the earth is flat," the clause is a modifier for "is".

It functions as an adverb the same way "as soon as" and "in order to".