In English, there are two basic types of words that are used to modify the subjects and objects in a sentence. Adjectives describe or modify nouns, and adverbs fulfill the same task for verbs. A relative adverb, while retaining its personality as an adverb in the strictest sense, introduces an adjective clause. Relative adverbs are the words when, where, and why. The purpose of a relative adverb is to modify the verb in the adjective clause.
The relative adverb when, of course is concerned with time in the relative sense. It can mean time in the future, as in “I will still love you when I’m 64,” or time in the past: “I was afraid of spiders when I was a child.” It can also be used to describe recurrent events, for example, “My mother always cries when Mother’s Day rolls around, and the family makes her dinner and gives her gifts.”
If when modifies verbs of time, where pinpoints place. Its function is to describe location. An example of this can be found in the statement “Ms. Beasley teaches fifth grade in the same school where her father used to be the principal.” In this sentence, the relative adverb where is used to describe the verb phrase "used to be." The adjective clause “where her father used to be the principal” modifies the noun school.
The relative adverb why suggests or provides a reason for something. It answers an asked or unasked question and modifies through clarification. An irritated mother might tell her children, “The reason why we aren’t going to the zoo today is because your rooms are a mess!” The adjectival phrase, “why we aren’t going to the zoo today” modifies the noun reason, while why modifies the verb phrase “we aren’t going.”
It’s important to recognize that these three verbs, where, when, and why, are most often used to ask questions. “Where did you put my bongo drum?” is a direct query. “Why won’t you answer my question?” seeks a response, as does the perennial favorite of children in the backseat of any car: “When do we get there?” Used in this way, these words are still adverbs but have shifted their name tags to read interrogative adverbs.
When they are functioning as relative adverbs, these same words aren’t asking questions. Their job, in this sense, is rather to pinpoint information. They are connectors, marrying two clauses into a single sentence.