Are adjective complement clauses considered to be adverbial?

Question

One: In school, we are often told that an adverb can modify, not only a verb, but also an adjective. So we have ...

i) verb modifier: The man leaped suddenly.
ii) adjective modifier: Suddenly afraid, Alice locked the door.

Two: Adverbial clauses can modify verbs.

iii) When the grunions come ashore, we all feast.

Three: Is a clause that serves as a complement or modifier of an adjective considered to be adverbial?

iv) That fish was so big (that) it almost swallowed the boat.

Or have I misanalyzed a lot of things here?

Answer 1

I think your i)-iii) are adverbs, but I don't agree about what they modify. I don't know about iv).

In i), it is the event of the man leaping, described by a sentence, which is modified by being said to be sudden. So "suddenly" modifies a sentence.

In ii), it is the inception of the state of Alice being afraid, described by a sentence, which is modified by being said to be sudden. So "suddenly" modifies a sentence. (Alternatively, perhaps it's the state of being afraid expressed by a verb phrase which is modified.)

In iii), it's the temporal relationship of two events that "when" concerns, each of the events described by a sentence: The grunions come ashore [at a certain time], and We all feast [at that time]. So the adverb "when the grunions come ashore" modifies the sentence "we all feast".

This is something that traditional grammarians are not good at, because somehow they've gotten the idea that modifiers always modify words. Often, adverbs modify phrases. In the typology of adverbs offered by McCawley in The Syntactic Phenomena of English, the only clause adverbs that modify verbs are adverbs of extent, such as "completely".