Commas with Nonrestrictive Clauses

A clause is nonrestrictive when it adds extra information about a noun without narrowing down which noun the sentence refers to. Put commas around that clause. A restrictive clause is needed to identify the intended person or thing, so it normally stays attached to the sentence without commas. This distinction often appears with relative clauses beginning with who, which, or that, but meaning—not the first word alone—determines the punctuation.

The remove-it test

Temporarily remove the clause. If the reader can still identify the intended noun and the main statement remains clear, the clause is likely nonrestrictive and should be set off with commas. If removing it changes which person, place, or thing is meant, the clause is restrictive and normally takes no commas.

How to punctuate the clause

• If the clause interrupts the sentence, use a comma before and after it: “The principal, who joined in August, introduced the plan.”
• If the clause comes at the end, place a comma before it: “We reviewed the proposal, which arrived yesterday.”
• If the clause begins the sentence, do not add a comma merely because it is a clause; punctuate according to the sentence structure and meaning.
• Do not place only one comma around a parenthetical clause in the middle of a sentence. The pair marks both edges.
• Do not use commas to set off a restrictive clause. The reader needs that information to know which noun is meant.

Who, which, and that

Many style guides use who for people, which for things in nonrestrictive clauses, and that for restrictive clauses. Standardized-test questions often use this pattern, but the strongest clue remains whether the clause is essential to identifying the noun. A sentence can also contain a nonrestrictive clause introduced by who. The commas still come from the clause’s function.

Compare “Students who finish early may leave” with “Students, who finished early, may leave.” In the first sentence, only the students who finish early may leave. In the second, the commas suggest that the identified students all finished early and may leave. When punctuation changes the scope of a statement, read the sentence carefully for the intended meaning.

Frequent comma errors

• Adding commas around a clause that selects one item from a larger group.
• Leaving out one comma when the clause interrupts the main sentence.
• Using a comma before every who, which, or that clause without checking its meaning.
• Treating a long clause as nonrestrictive just because it is long. Length does not determine whether it is essential.
• Confusing a nonrestrictive clause with an introductory phrase; each structure follows a different punctuation pattern.

A quick editing routine

1. Underline the noun the clause describes.
2. Ask whether the clause tells the reader which noun is meant.
3. If it identifies the noun, keep it restrictive and omit the commas.
4. If it adds information about an already identified noun, place commas at both boundaries.
5. Read the sentence aloud and confirm that the comma choice matches the intended meaning.

Key takeaway

Use commas around a nonrestrictive clause because it adds optional information. Leave a restrictive clause unpunctuated because it identifies the noun. The remove-it test helps reveal which job the clause is doing.

Set off information that can be removed

A nonrestrictive clause adds information about a noun already identified. It is usually introduced by which or who and enclosed by commas: “The handbook, which was revised in June, includes the new process.” Remove the clause and the reader still knows which handbook is meant. The commas show that the information is additional rather than identifying.

A restrictive clause identifies which person or thing the writer means and is not set off: “The handbook that was revised in June includes the new process.” This implies that several handbooks may exist and the June revision distinguishes one. The difference is not just punctuation; it changes the reference and sometimes the meaning.

Use paired commas around an interruption

If a nonrestrictive clause appears in the middle of a sentence, use a comma at both boundaries: “The handbook, which was revised in June, includes the new process.” One comma alone leaves the sentence’s structure unfinished. At the end of a sentence, a comma before the clause may be enough: “We used the handbook, which was revised in June.”

A clause beginning with that is generally restrictive in standard American usage, while which is commonly used for nonrestrictive clauses. Who refers to people. Some publications use which in restrictive clauses, so follow a stated style guide; the essential distinction is whether the clause identifies or merely adds information.

Check meaning before adding commas

The removal test is helpful but not mechanical. If removing the clause changes which person or thing is being discussed, the information is restrictive. If it only removes a side detail, it is nonrestrictive. A sentence can be ambiguous when the writer’s intended reference is unclear; revise the noun phrase instead of relying on punctuation alone.

Use commas with nonrestrictive clauses in the same way whether the clause appears at the beginning, middle, or end, adjusting for sentence structure. Do not confuse a nonrestrictive clause with a short introductory dependent clause or an appositive phrase; all may use commas, but they have different grammatical forms.

• Ask whether the clause identifies the noun or adds side information.
• Set off nonrestrictive clauses with commas.
• Do not comma off a restrictive clause needed to identify the noun.
• Use paired commas around an interruption.
• Revise if punctuation alone cannot make the intended reference clear.

Apply the distinction carefully

A nonrestrictive clause adds information that the reader does not need to identify the noun. Set it off with commas on both sides when it appears within a sentence: “The school library, which reopened in August, now offers evening hours.” Removing the clause leaves the identifying reference intact. A restrictive clause identifies which person or thing is meant and normally takes no commas: “Libraries that offer evening hours serve working students.” Here the clause narrows the set of libraries. Read the sentence without the clause and ask whether the remaining noun phrase still identifies the intended referent. Meaning guides the punctuation; the word which or that alone is not a reliable substitute for that test.