In the sentence, "Sylvia looks good in her mermaid costume" why is good the correct word used as an adjective, as opposed to using well as an adverb. Isn't "good" describing how Sylvia looks?

The adjective "good" describes Sylvia. Since "looks" is a linking verb in this sentence, the correct complement is the adjective.

You're correct in recognizing that "good" is an adjective in the given sentence, and it is used to describe how Sylvia looks. The reason for using "good" instead of "well" in this context lies in the distinction between adjectives and adverbs.

While both adjectives and adverbs can be used to provide information about appearance, adjectives specifically modify nouns, pronouns, or noun phrases. In this case, "good" modifies the noun phrase "Sylvia," specifying the quality of her appearance. It tells us what kind of appearance Sylvia has.

On the other hand, adverbs, like "well," typically modify verbs, adjectives, or other adverbs. They provide more information about how an action is performed or how a verb is happening.

In this particular sentence, the focus is on describing Sylvia's appearance, not how she looks. Hence, the adjective "good" is correct because it directly describes Sylvia. If we were to use "well" as an adverb, it would imply that Sylvia has the ability to look in a skilled or satisfying manner, which doesn't convey the intended meaning.