While adjectives almost always have some relationship to a noun, whether in the NP or the VP, adverbs modify many other parts of speech; classically, adverb phrases (AdvP) are understood as ‘modifying’ verbs in verb phrases, where they appear as adjuncts, but they can also modify adjective phrases, prepositional phrases, other adverb phrases, and both main and subordinate clauses as well.
In what way are adverbs different from adjectives in terms of what parts they can change?