Defining (essential) relative clauses

A relative clause is a mini-sentence stuck onto a noun to tell you more about it. The man who lives next door is a doctor. The bold part is the relative clause — it modifies the man.

There are two kinds: defining (essential to identify which one) and non-defining (extra info, removable). This lesson covers defining clauses — the kind that does real work picking out which person or thing you mean. Non-defining clauses get their own lesson next.

The marker of a defining clause: no commas. The clause is welded to the noun.

What “defining” means

A defining clause answers the question which one? Without it, the listener wouldn’t know which person or thing you’re talking about.

The book that I bought yesterday is excellent.

If you remove the bold part — The book is excellent — the listener has no idea which book. The defining clause is essential.

Compare:

My brother, who lives in Boston, is a doctor. (non-defining — I only have one brother; the clause is just extra info) The brother who lives in Boston is a doctor. (defining — I have multiple brothers; the clause specifies which)

The grammar shifts with the meaning. No commas signals “you need this to know who I mean.”

The pronouns

In defining clauses, that is extremely common — and in American English, often preferred over which. More on that below.

Subject vs object — the omission rule

A relative pronoun can play one of two roles inside its clause: subject of the clause’s verb, or object of it. This determines whether you can drop the pronoun.

Subject — keep the pronoun

The pronoun is doing the action.

The man who called me is my boss. — who is the subject of called. The book that won the prize was boring. — that is the subject of won.

You cannot omit the pronoun here. The man called me is my boss — wrong.

Object — drop the pronoun (optional)

The pronoun receives the action; another subject does the verb.

The book (that) I read was excellent. — I is the subject; that is the object of read. The woman (who/that) you met yesterday is a teacher. — you is the subject; who/that is the object of met.

In casual American English, dropping the object pronoun is the default:

• The book I read.
• The movie we saw.
• The guy you talked to.

Keeping it (The book that I read) sounds slightly more careful or formal — both are correct.

Quick test: is there already a subject after the pronoun?

If a new subject appears right after the relative pronoun, the pronoun is the object — you can drop it.

Whose — possession

Whose shows ownership and works for both people and things.

• The student whose laptop was stolen got a new one. (the laptop belongs to the student)
• I have a friend whose father is a chef.
• We bought a house whose roof needs repair. (also OK for things, though the roof of which is more formal)

Whose cannot be dropped. It’s both showing possession and connecting clauses — too important to omit.

Where, when, why — adverbial relatives

These replace in/at + which for places, times, and reasons.

The short form is much more common in conversation. The long form sounds formal / written.

You can also drop where / when / why in casual speech when context is clear:

• That’s the day (when) I met her.
• The reason (why) I called is…
• The place (where) I work is downtown. (more often kept here)

That vs which — the AmE preference

In defining clauses, American English strongly prefers that over which for things. This is a real stylistic rule — not just preference but actively taught in American style guides (Strunk and White, Chicago, AP).

In AmE writing, which is reserved almost exclusively for non-defining clauses (with commas — see next lesson):

• My laptop, which I bought last year, is broken. — non-defining, which is correct.
• The laptop that I bought last year is broken. — defining, that is preferred.

In British English, which is freely used in defining clauses too. In AmE, using which in a defining clause sounds slightly stiff or British.

For people, who and that are both fine in defining clauses; that is slightly more casual.

• The woman who called. (slightly more formal)
• The woman that called. (slightly more casual)
• The woman called — wrong, can’t omit subject.

Prepositions in defining clauses

When the relative pronoun is the object of a preposition, you have two patterns.

Informal (more common)

Preposition stays at the end of the clause; pronoun can be dropped.

• The man (that) I work with.
• The book (that) I told you about.
• The chair (that) you’re sitting on is broken.

Formal

Preposition + whom / which moves to the front; pronoun cannot be dropped.

• The man with whom I work.
• The book about which I told you.
• The chair on which you’re sitting is broken.

In speech and most writing, the informal pattern wins. The formal pattern shows up in legal, academic, or very polished writing. Whom (formal object form of who) is fading from spoken AmE; learners can stick with who or that.

When that must be used (or strongly preferred)

A few cases where that is the standard choice in defining clauses:

Using which or who here sounds odd — the best book which I’ve ever read feels off.

Animals — which or that, sometimes who

Pets and named animals often take who (treating them as people). Wild or generic animals usually take which / that.

• My dog Bella, who loves the beach… (pet, named, personified)
• The bird that sings outside my window.
• Animals which live in cold climates.

This isn’t a hard rule — speakers vary based on emotional closeness to the animal.

AmE notes

• Strong preference for that in defining clauses. AP and Chicago style guides actively recommend that over which when no commas. Editors will often “correct” which to that in American manuscripts.
• Whom is rare in speech. The man whom I met sounds bookish; most Americans say the man (that) I met or the man who I met.
• Object pronoun omission is the default in casual speech. The book I bought, the movie we saw, the guy I told you about — drop the relative pronoun unless you want to sound careful.
• Stranded prepositions are normal. The person I’m working with sounds natural; the person with whom I’m working sounds like a textbook.

Pronunciation notes

• that in a defining clause reduces to /ðət/ when unstressed: The book that I read → /ðə bʊk ðət aɪ rɛd/.
• who /hu/ keeps its full vowel; whose /huz/ — voiced final.
• which /wɪtʃ/ — the wh in AmE is just /w/ (no breathiness).
• When the pronoun is omitted, the noun phrase flows directly into the next clause: The book I read → /ðə bʊk aɪ rɛd/, no pause where that would have been.

Common Russian-speaker mistakes

1. Doubled subject — pronoun copy. My brother who lives in Boston he is a doctor → My brother who lives in Boston is a doctor. Russian often repeats the subject after a long modifier; English forbids it. The relative clause already attaches to brother; no second pronoun needed.
2. Using what instead of that / which. The book what I read → The book (that) I read. In Russian, что covers both “what” and “that”; in English, what is for questions and “the thing(s) which” — never as a relative pronoun for a defined noun.
3. Dropping the subject pronoun. The man called me is my boss → The man who called me is my boss. You can only drop the pronoun when it’s the object (a new subject follows). Subject pronouns are mandatory.
4. Omitting that after superlatives feels wrong but is sometimes done — leave it in for clarity. The best book I’ve ever read is grammatically fine, but in formal writing keep that: The best book that I’ve ever read.
5. Using which for people. The woman which called → The woman who (or that) called. Which is for things/animals only.
6. Wrong word order with prepositions in informal speech. The man with that I work → The man (that) I work with. In informal AmE, the preposition moves to the end of the clause.

Summary

• Defining = essential (no commas); non-defining = extra info (commas — next lesson).
• Pronouns: who (people), which (things), that (both), whose (possession), where / when / why (place / time / reason).
• Drop the pronoun when it’s the OBJECT of the clause’s verb (a new subject follows it). Cannot drop SUBJECT pronouns.
• AmE prefers that over which in defining clauses; reserve which for non-defining.
• Whose and superlative-triggered that cannot be dropped.
• Stranded prepositions (informal: the person I work with) are normal in AmE.

Next lesson: non-defining relative clauses — the comma-set-off kind, where that is forbidden and which takes over.