Relative Clauses: Meaning, Pronouns, and Commas

Quick Answer

A defining relative clause supplies information needed to identify the referent and takes no commas: The files that contain signatures are archived.

A non-defining relative clause adds information about an already identified referent and is set off with commas: The signed contract, which is in the archive, expires Friday.

Then choose who, whom, whose, which, that, where, or when from the referent, clause type, and the connector's grammatical role.

Reference Before Punctuation

Do not ask only whether a sentence remains grammatical after deletion. Ask whether deleting the clause changes which referent the noun phrase identifies.

The Defining/Non-Defining Decision

Question	Defining	Non-defining
What does the clause do?	identifies or limits the referent	adds information about an identified referent
Punctuation in writing	no surrounding commas	commas around an inserted clause
Can that introduce it?	yes	no
Can an object pronoun be omitted?	often	no

One sentence pair, two reference structures

Defining subset:

The engineers who completed training can deploy.

Already identified group:

The release engineers, who completed training, can deploy.

The first clause selects engineers by a condition. The second presents the training fact as supplementary information about the already named release engineers.

Choose the Connector by Referent and Role

Connector	Referent or role	Clause types	Boundary
who	people; sometimes pet animals	defining and non-defining	subject or object
whom	people	defining and non-defining	formal object form; used after a fronted preposition
whose	possessive relation	defining and non-defining	people and animals; sometimes things in formal contexts
which	animals and things	defining and non-defining	also used after a fronted preposition
that	people, animals, and things	defining only	not after a fronted preposition
where / when	place / time relation	defining and non-defining	can replace a matching preposition-plus-which relation

Cambridge records both which and that in defining clauses about things. The grammatical boundary is not “which always means commas”; it is that that does not introduce a non-defining relative clause.

Find the Gap Inside the Clause

Rebuild the relative clause as a plain sentence. The missing job tells you whether the connector is a subject, object, or possessive determiner.

Relative clause	Plain reconstruction	Role	Omission?
the editor who approved it	the editor approved it	who = subject	no
the draft that we approved	we approved the draft	that = object	yes, in this defining clause
the report whose appendix changed	the report's appendix changed	whose = possessive	no

Omitting the object gives the draft we approved. Omitting the subject produces the broken sequence the editor approved it resigned.

Preposition Placement Changes the Available Form

Fronted preposition

Formal structure:

The colleague to whom I spoke replied.

A fronted preposition can precede whom or which, but not that.

Preposition at the end

Defining clause:

The colleague who I spoke to replied.

Object omitted:

The colleague I spoke to replied.

In a defining clause, an object connector can be omitted when the preposition remains at the end.

Four Structural Repairs

Person mismatch:

The manager which approved the budget resigned.

Person subject:

The manager who approved the budget resigned.

Who fills the subject role and refers to a person.

Non-defining with that:

The budget, that was revised, passed.

Non-defining connector:

The budget, which was revised, passed.

The comma-delimited supplementary clause uses which, not that.

Repeated subject:

The school that it teaches Latin is closing.

One subject:

The school that teaches Latin is closing.

That already serves as the relative clause's subject.

Repeated object:

The report which Maya revised it is final.

One object:

The report which Maya revised is final.

Which already supplies the object gap; do not repeat it with it.

Test Reference, Role, and Omission

1. The analyst ____ built the model will present it.

2. The model, ____ was rebuilt yesterday, is stable.

3. The study ____ methods were challenged was withdrawn.

4. In “the draft that we revised,” may that be omitted?

5. In “the draft that changed,” may that be omitted?

Exact Check: The Referent Mismatch Passed Unflagged

On July 16, 2026, the exact person-plus-which seed below returned no issues. The manual revision with who also returned no issues.

Exact tested seed:

Manual source-backed revision: The manager who approved the budget has resigned.

This pair documents one contextual false negative and one accepted revision. It does not establish behavior for commas, omission, repeated pronouns, other antecedents, or every connector.

Frequently Asked Questions

What makes a relative clause defining or non-defining?

A defining relative clause supplies information needed to identify the referent and takes no commas. A non-defining clause adds information about an already identified referent and is set off with commas. Test the intended reference, not whether the shortened sentence is merely grammatical.

Can which introduce a defining relative clause?

Yes. Cambridge records both which and that in defining clauses about things. In a non-defining clause about a thing, use which and commas; that does not introduce that clause type.

Can that introduce a non-defining relative clause?

No. Cambridge and the British Council both exclude that from non-defining relative clauses. Use who, which, whose, whom, where, or when as the meaning and grammatical role require.

When can I omit a relative pronoun?

You can often omit an object relative pronoun in a defining clause: the report that we revised becomes the report we revised. Keep a subject relative pronoun, and keep the connector in a non-defining clause.

Can whose refer to a thing?

Yes. Cambridge records whose for people and animals and sometimes for things in formal situations. The phrase whose findings were disputed is therefore not limited to a human antecedent.

Boundary Examples

Defining subject:

Tickets that include lunch cost more.

The clause identifies a subset; that is its subject.

Defining object:

The tickets we bought include lunch.

The omitted connector would be the object of bought.

Non-defining person:

Priya, who bought the tickets, kept the receipt.

The clause supplements an already named referent.

Non-defining thing:

The receipt, which is digital, is in the email.

Which introduces the comma-delimited clause.

Possession:

The report whose appendix is missing needs revision.

Whose links the appendix to the report.

Place relation:

The lab where we tested it has reopened.

Where expresses the place relation.

Fronted preposition:

The method by which we tested it is documented.

Which, not that, follows the preposition.

Missing subject:

The file contains signatures is archived.

Restore the subject connector: The file that contains signatures is archived.

Direct Sources and Scope

Cambridge's defining and non-defining relative clause guide supports the information, punctuation, pronoun, omission, and meaning-pair boundaries. Its relative pronoun guide supplies the referent-and-role table, object omission, and preposition restrictions.

The Cambridge page on typical relative clause errors supports the repeated-subject, repeated-object, and comma repairs. The British Council's non-defining relative clause lesson independently supports required connectors, comma separation, the exclusion of that, and place/time relations.

These sources do not establish how often writers make each error, which rule readers notice most, or which untested sentences the checker catches. Those claims have been removed.

A Five-Step Relative Clause Audit

Underline the antecedent. Identify the person, animal, thing, place, or time being described.
Decide the reference. Does the clause identify the referent, or add information about one already identified?
Rebuild the gap. Determine whether the connector is the subject, object, possessive determiner, or place/time relation.
Choose connector and punctuation together. Apply the clause-type and referent boundaries before adding or removing commas.
Check for duplication or omission. Remove repeated subjects or objects, but keep a required subject and every non-defining connector.

How This Page Differs from the Narrow Guides

The which versus that guide focuses on one connector pair. The who versus that guide focuses on human reference, while the who versus whom guide focuses on case. The comma rules guide covers punctuation broadly.

This page connects all four problems through antecedent, clause type, gap role, omission, preposition placement, and one exact checker limitation.

Check the Surface, Then Rebuild the Clause

Use the checker for sentence-level feedback, then apply the five-step audit when meaning and grammatical role determine the result.

Try Grammar Checker Free →