Relative clauses (also known as adjective clauses or adjectival clauses) are dependent clauses that provide descriptive information about a noun or noun phrase. Relative clauses are introduced by either a relative pronoun or a relative adverb, and the information they provide can either be essential or nonessential to the completeness of the sentence.
Relative Pronouns and Relative Adverbs
Relative pronouns are used to help clarify who or what a sentence is talking about, or else give extra information about the person or thing. Like other pronouns, they have the grammatical function of nouns, and can be either the subject or object of the relative clause. There are five common relative pronouns: who, whom, which, whose, and that.
Here are some examples of relative clauses introduced by relative pronouns:
- “There’s the woman who sits next to me on the bus.”
- “The man, whom I’d heard so much about, gave an electrifying speech to the crowd.”*
- “The escaped giraffe, which had been on the loose for weeks, was finally captured.”
- “The book that I wrote is being published in January.”
- “Any student whose desk is not clean will have detention after class.”
Relative adverbs, on the other hand, are used when the information relates to a place, time, or the reason an action took place; like many other adverbs, they modify a verb in the sentence. The relative adverbs are where, when, and why.
- “The house where I was born is a very special place.” (Where modifies the verb born.)
- “I love casual Fridays, when we get to wear jeans to work.” (When modifies the verb wear.)
- “I don’t know why he got so angry.” (Why modifies the verb get.)
(*Usage Note: Whom is becoming increasingly rare in modern English outside of formal writing or speech. Although it is technically correct to use whom when it functions as the object of a clause and who when it functions as the subject, it is much more common to use who in both cases.)
Restrictive and Non-restrictive Clauses
Clauses that provide essential information are known as restrictive clauses (sometimes also called defining clauses), while those that provide nonessential information are known as non-restrictive clauses (sometimes called non-defining clauses). Because non-restrictive clauses are not integral, they are separated from the rest of the sentence by commas.
Restrictive relative clauses
Restrictive relative clauses identify a particular noun, giving us information about it that we need to know in order to understand the speaker’s meaning. Because this type of clause is integral to the sentence, it is not separated by any punctuation. For example:
- “I saw the guy who delivers my mail in town yesterday.”
- “I’ll always remember the river where we learned to swim.”
- “Yesterday was the day when I met my husband.”
- “I sat on the chair that has a wobbly leg.”
- “Do you know the reason why the sky is blue?”
- “She’s the person whose daughter goes to Harvard.”
The restrictive relative clause in each of the sentences above is in bold. If we remove the relative clause, we are left with questions about who or what the speaker is referring to:
- “I saw the guy in town yesterday.” (What guy?)
- “I’ll always remember the river.” (What river?)
- “Yesterday was the day.” (What day?)
- “I sat on the chair.” (What chair?)
- “Do you know the reason?” (The reason for what?)
- “She’s the person.” (What person?)
When you remove a restrictive relative clause, the nouns are no longer identifiable and the sentences become logically incomplete.
It is worth noting that the relative pronoun which is not used to introduce restrictive relative clauses. However, the authenticity of this rule is often contested, and modern writers very often use which and that interchangeably with restrictive clauses. If you have any doubts, though, especially in formal or professional writing, then it is better to reserve which for non-restrictive clauses.
Non-restrictive relative clauses
Non-restrictive relative clauses give us additional information about a noun that has already been identified, but this information is not essential for the sentence to make sense. Because of this, non-restrictive relative clauses are set apart from the rest of the sentence by commas.
- “Paris, where I spent six months studying, is the most beautiful city in the world.”
- “The woman down the street, whose children are the same age as ours, invited us over for dinner next week.”
- “I love casual Fridays, when we get to wear jeans to work.”
- “Samantha, whom I’ve asked to be my bridesmaid, is getting married next year.”
- “The senator, who is up for re-election next month, has made a lot of promises to his constituency.”
- “The movie, which is my favorite comedy of all time, is being shown on TV tomorrow night.”
In the examples above, the relative clauses merely give extra information about the nouns; they do not define them. The sentences would still make sense even if the relative clauses were removed, which is how we know that we are dealing with non-restrictive relative clauses. For example:
- “Paris is the most beautiful city in the world.”
- “The woman down the street invited us over for dinner.”
- “I love casual Fridays.”
- “Samantha is getting married next year.”
- “The senator has made a lot of promises to his constituency.”
- “The movie is being shown on TV tomorrow night.”
Note that non-restrictive clauses cannot be introduced by the relative pronoun that or the relative adverb why—these can only introduce restrictive clauses.