Non-defining (extra info) relative clauses

In the last lesson you met defining clauses — the no-commas kind that picks out which one. This lesson covers the other half: non-defining clauses, which add extra information about an already-identified noun.

The hallmark is commas — one before the clause, one after (unless the clause ends the sentence). Visually, the commas signal “remove this and the sentence still works.”

My brother, who lives in Boston, is a doctor. Strip the bold: My brother is a doctor. Sentence still complete; you just lost some background detail.

This is the structure used in news writing, business prose, biographies — anywhere you want to slip in supplementary info without breaking the main flow.

The defining vs non-defining test

Same words, different commas, different meaning:

My sister who lives in Boston is a doctor. — Defining. I have multiple sisters; the clause specifies which one. My sister, who lives in Boston, is a doctor. — Non-defining. I have one sister; the clause adds info about her.

The commas aren’t decorative — they change the truth conditions of the sentence. Get them right.

A useful test: Could you remove the clause without losing essential meaning?

• Yes → use commas (non-defining).
• No → no commas (defining).

Steve Jobs, who founded Apple, died in 2011. (one Steve Jobs we mean — extra info, commas) The man who founded Apple died in 2011. (which man? — defining, no commas)

The pronouns

Mostly the same as defining, with one big exception.

Notice what’s missing: that. That is forbidden in non-defining clauses. This is one of the few hard rules of English relative-clause grammar.

❌ Boston, that is in Massachusetts, has great seafood. ✅ Boston, which is in Massachusetts, has great seafood.

❌ My father, that is 70, still works. ✅ My father, who is 70, still works.

If you see commas, that is wrong. Use who / which / whose / where / when.

You also can’t omit the pronoun

Another defining-vs-non-defining contrast: in non-defining clauses, the relative pronoun is never optional, even when it’s the object.

❌ The book, I bought yesterday, is on the table. ✅ The book, which I bought yesterday, is on the table.

The pronoun has to be there to anchor the clause to its noun across the comma break.

Where the commas go

• Mid-sentence: comma before AND after the clause. My sister, who lives in Boston, is a doctor.
• End of sentence: comma before; period (or other terminal punctuation) closes it. I called my sister, who lives in Boston.

In speech, you can hear the commas: a slight pause and a flatter pitch on the inserted clause.

My sister — pause — who lives in Boston — pause — is a doctor.

If you’d say it without those pauses, you probably mean the defining version (no commas).

Which referring to a whole clause

A special and very useful trick: which can refer back to the entire previous clause, not just a noun. This use is only non-defining (always with a comma).

He arrived late, which annoyed everyone. ↑ which = “the fact that he arrived late”

She got the promotion, which surprised no one. They cancelled the flight, which ruined our plans. He didn’t apologize, which I found rude.

This pattern is extremely common in commentary, opinion writing, and casual speech. The comma is mandatory.

Compare:

• He arrived late, which annoyed everyone. (the lateness annoyed everyone)
• He arrived late, that annoyed everyone. — wrong, that never used here.
• He arrived late, and that/it annoyed everyone. — alternative phrasing, also fine.

This use is one of the strongest reasons to learn the which / that distinction: in this construction, only which works.

Prepositions in non-defining clauses

You have the same two patterns as in defining clauses — formal (preposition + whom/which fronted) vs informal (preposition stranded at the end).

Formal

Mr. Smith, with whom I work, is retiring. The proposal, about which I have concerns, is on the agenda. 2020, in which the pandemic began, was unforgettable.

Informal / conversational

Mr. Smith, who I work with, is retiring. The proposal, which I have concerns about, is on the agenda.

In casual American speech, the stranded version dominates. The fronted with whom / about which version is reserved for formal writing — legal, academic, very polished business prose.

Whom in particular is fading from spoken AmE but survives in writing after prepositions.

Whose and of which

For possession with things, whose is grammatically allowed but sometimes feels odd; an alternative is of which.

The book, whose cover is torn, is on the shelf. The book, the cover of which is torn, is on the shelf. (more formal)

For people, whose is the only natural choice:

Maria, whose father is Spanish, is bilingual.

Stacking non-defining clauses

You can chain non-defining clauses, but use them sparingly — too many and the sentence becomes hard to read.

My uncle Tom, who lives in Texas, whose wife is a chef, is visiting next week. — possible but heavy.

Better: split it.

My uncle Tom, who lives in Texas, is visiting next week. His wife, who is a chef, is coming too.

In good writing, one non-defining clause per noun is plenty.

Where you’ll see this most: news and business writing

Non-defining clauses are everywhere in journalism, biographies, business reports — anywhere a writer needs to give background without slowing the main idea.

The CEO, who has led the company since 2019, announced his resignation Tuesday. Apple, which is headquartered in Cupertino, posted record earnings. Mars, the fourth planet from the Sun, may have once had liquid water. (this is an appositive — same idea, no relative pronoun, very common)

Compare to spoken English, where non-defining clauses are less frequent but still common in storytelling and explanations:

I called my sister — you know, the one who lives in Boston — and she said…

AmE notes

• More comma usage than BrE. American style guides (Chicago, AP) lean toward more punctuation around inserted material. If you’re uncertain, the AmE tendency is to add commas.
• Strict that / which split. AmE style guides enforce: that for defining (no commas), which for non-defining (with commas). British writing is looser. Editors at AmE publications will reliably “correct” which to that in defining clauses and flag that in non-defining clauses.
• Common in business and email writing. The proposal, which we discussed last week, needs revisions. This pattern is everyday corporate prose.
• Stranded prepositions are normal. Mr. Smith, who I work with sounds natural; with whom I work sounds like a court filing.
• Whom-avoidance. Most American speakers say my friend, who I called yesterday even though whom is technically the object form. Whom is increasingly limited to formal writing immediately after a preposition.

Pronunciation notes

• The commas correspond to prosodic breaks — small pauses and a flatter, lower pitch on the inserted clause.
• which /wɪtʃ/ — fully voiced; the wh is just /w/ in AmE.
• who /hu/, whose /huz/, whom /hum/ — keep the full /u/ vowel.
• In which annoyed everyone-type clauses (referring back to a whole idea), the which is often slightly stressed: He arrived late, WHICH annoyed everyone.

Common Russian-speaker mistakes

1. Using that in non-defining clauses. Boston, that is in Massachusetts, has great seafood → Boston, which is in Massachusetts, has great seafood. That is forbidden after a comma. Always who / which / whose.
2. Missing commas — turning non-defining into defining and changing the meaning. My brother who lives in Boston is a doctor (defining: I have multiple brothers) is grammatically fine but means something different from My brother, who lives in Boston, is a doctor (one brother, extra info). Add commas when you mean extra info.
3. Doubled subject — pronoun copy. My friend, who lives in NYC, she is a teacher → My friend, who lives in NYC, is a teacher. Same Russian-style copy as in defining clauses.
4. Using what instead of which for whole-clause reference. He arrived late, what annoyed everyone → He arrived late, which annoyed everyone. What never works as a relative pronoun pointing back to a clause.
5. Omitting the pronoun in non-defining clauses. My laptop, I bought last year, is broken → My laptop, which I bought last year, is broken. In non-defining clauses, the pronoun is mandatory even when it’s the object.
6. Confusion with who vs whom. In speech, just use who: My boss, who I called yesterday, was busy. Whom is increasingly formal-only and not required in everyday AmE.

Summary

• Non-defining = extra info, set off by commas; remove the clause and the sentence still makes sense.
• Never use that after a comma; use who / which / whose / where / when.
• The pronoun is never optional in non-defining clauses, even as object.
• which can refer back to a whole previous clause: He arrived late, which annoyed everyone.
• AmE writing: strict split — that for defining (no commas), which for non-defining (with commas).
• Stranded prepositions are normal in conversational AmE; fronted with whom / about which is for formal writing.

Next lesson: gerund vs infinitive — the full system — finally untangling enjoy reading vs want to read and the confusing meaning-changing verbs.