A word doesn’t necessarily belong to one part of speech. Depending on how it is used in a sentence, it can belong to more than one. Same goes with how, which can be an adverb or a noun (rarely).
1. How as adverb
How can be an interrogative adverb: interrogative because it is in the form of a question (direct or indirect) and adverb because it conveys information about manner (how fast?), time (how soon?), degree (how good?), etc. If you recall, adverbs convey information about time, place, manner, degree, reason, etc. Examples:
(Comments are in square brackets.)
How are you doing?
How quickly can you finish the task?
I know how noun clause works. [Indirect question. It’s also known as wh-noun clause]
How I passed the test is a story in itself. [Indirect question]
I advised my friend on how to improve his fitness. [Indirect question. It’s a non-finite clause though]
Note that unlike other interrogative adverbs (when, where, and why), how is not a relative adverb.
Some mistakenly treat how introducing a noun clause as subordinating conjunction. That’s because, in common parlance, the term subordinating conjunction is associated with any word that joins a dependent clause to an independent clause. But in noun clauses, none of wh-elements (how, when, where, why, who, whom, whose, what, which) is a subordinating conjunction. They are either interrogative adverb (how, for example), interrogative pronoun, or interrogative determiner.
To summarize what we’ve covered so far:
- How introducing a direct or an indirect question (noun clause) functions as interrogative adverb
If you noticed, how introduces only one dependent clause – noun clause. Since it doesn’t introduce relative clause, it’s not a relative adverb. And since it doesn’t introduce adverb clause, it’s not a subordinating conjunction.
2. How as noun
How can sometimes be a noun. Examples:
The mother struggled to answer the whys and hows of the kid.
I’ve always been more interested in the how of any recipe.
Summary
How mainly functions as an adverb (interrogative), but on rare occasions it can function as a noun:
How much does this cost? [Interrogative adverb in a direct question]
I don’t know how much this costs? [Interrogative adverb in an indirect question (noun clause)]
This item is so expensive. Can anyone tell me the how and why of its price? [Noun]
Will you please explain the role of AS and HOW in the following sentences? Are both of the sentences correct?
This is HOW it should be.
This is AS it should be.
Thank you for your help.