Getting tangled up in relative clauses is easy enough to do. Their use often presents a couple of knotty issues that perplex those of us on the far side of eighth-grade grammar class. Many of us, moreover, incorporate into our own grammar some of the structures we hear and read, usually without realizing whether those structures are correct.

A clause, remember, is a group of words that contains a subject and a predicate. Some clauses are independent—that is, they could stand alone as sentences. Others are dependent or subordinate; they rely on an independent clause (a sentence) to complete their meaning.

A relative clause offers a way of supplying additional information—usually a definition or an identification—to a noun or pronoun that comes right before it in a sentence. Unlike an appositive phrase, which modifies an entire sentence or clause, a relative clause refers to one word only. That word must be the noun or pronoun (person, place, idea, thing) that precedes it.

Relative pronouns (who, whom, that, which, whose) as well as relative adverbs (when, where) can signal the start of a relative clause. Such clauses indicate the relation of one part of the sentence to another; the difficulties they pose lie in choosing the correct relative pronoun/adverb and in punctuating the clause appropriately.


In formal English, the standard for most business writing and presenting, follow the rules. Doing so helps you meet audience expectations as well as ward off misinterpretation. In formal English, use:

  • Who and whom for people
    • The professor who holds the patent donates its royalties to the university where she studied.

  • When only for times or time periods
    • Those were the years when her hunger for science sharpened, she said.

  • Where only for places
    • The university named the laboratory where she worked after her.

  • Which for anything except people
    • She cherishes the honor, which is one among many.

  • That and whose for people or things
    • She sometimes visits the laboratory, whose equipment upgrades have been financed in part by her donations.


1. Relative clauses that provide information essential to understanding the meaning of the sentence do not contain commas.

  • The section that received closest scrutiny listed only three adverse events.
    • (The clause identifies which section listed the events so is essential to the sentence's meaning.)

  • The strongest support for the regulation came from the participant who had previously opposed it.
    • (The clause identifies which participant so is essential to the sentence's meaning)

2. When the relative clause provides information that is not essential to understanding the meaning of the sentence, use commas to set off the extra information.

  • Our team, which was assigned the project last year, asked for an additional financial analyst.
    • (The clause is set off by commas because it adds non-essential information; knowing when the project was assigned is not essential to the sentence's meaning.)

  • Usually the directions include landmarks, which make finding the turnoff much easier.
    • (The clause neither defines nor identifies the noun it refers to; instead, it adds extra information that is not essential to the sentence's meaning.)

Some grammarians recommend using "that" only in essential clauses and "which" for those that are non-essential. Others don't think it matters. But what matters to all is comma use. A relative clause beginning with "which" always requires commas. A "that" clause never does.

As you compose, display your competency not only in reasoning and organizing but in using correct grammar. You'll heighten your credibility and your readers' understanding of your position and messages. That's a good space for a writer to occupy.