Adjectives and adverbs describe (modify the meaning of) other words in a sentence. Adjectives modify nouns or pronouns. Therefore:
A word (or construction) that describes a noun or pronoun functions as (and therefore is) an adjective.Adverbs modify verbs, adjectives, or other adverbs. Therefore:
A word (or construction) that describes a verb, an adjective, or another adverb functions as (and therefore is) an adverb.
"A," "an," and "the" always function
as adjectives. "A" and "an" indicate that the word modified refers
to anything named by the noun or to something that is not specifically
known to the person spoken to.
In order to tell if a word is an adjective or an adverb, you must first look at the word in the context of a sentence. Thus, in the sentence
The little swan proudly blew his trumpet.
"The" and "little" are adjectives because they describe
the noun "swan." "Proudly" describes how he "blew." Since "blew" is a verb,
"proudly" is an adverb. Similarly, "his" describes the noun "trumpet,"
so "his" is an adjective.