Defining relative clauses

A defining relative clause tells you which person or thing you mean — take it away, and the sentence loses essential information, or stops making sense at all:

The woman who lives next door is a doctor. Without the clause, the woman could be anyone. The clause is what tells you which woman.

If you already know who, which and that for simple cases, this article builds on that with two more pronouns — whose and whom — and shows how a relative clause can be built around a preposition.

The quick version: a defining clause narrows down the noun and needs no commas. Alongside who / which / that, this article adds whose for possession (a genuinely everyday word) and touches on whom and fronted prepositions, which are more at home in formal writing than in everyday speech.

Why "defining"?

A defining relative clause defines — it picks the noun out of a group. Here's the contrast:

• The students who finished early could leave. — only some students, the ones who finished early.
• My brother, who lives in Berlin, is visiting next week. — extra detail about one specific brother, often implying there is only one brother, or that it's already clear which one is meant.

The second kind (with commas, adding non-essential extra detail) is a non-defining relative clause — a related but different structure, for a later topic. Apart from that one contrast example, every clause from here on is defining: no commas, and removing the clause changes who or what the sentence is about.

Whose: showing possession

Whose replaces a possessive determiner or genitive before a noun (his, her, its, their, or X's), and works for both people and things:

• That's the man. His dog barks all night. → That's the man whose dog barks all night.
• I met a writer. Her first novel became a bestseller. → I met a writer whose first novel became a bestseller.
• The company whose logo you saw is opening a new office.

In a relative clause, whose comes directly before a noun: ✅ the man whose dog barks, never ❌ the man whose barks.

Whom: the formal object pronoun

Whom is the object form of who, used for people when they are the object of the clause (not the subject). It sounds more formal than who or that, and is common in writing and after a preposition:

• The professor whom I emailed replied quickly. (more formal than the professor who/that I emailed)
• The guests whom we had invited earlier arrived first.

When the pronoun is the object of the clause, everyday spoken English usually prefers who or that — or dropping the pronoun altogether, as in the basic relative clauses article: the professor I emailed, the professor who I emailed. Whom is best kept for formal writing — it's the pronoun standard English uses for people directly after a preposition, the way which is used for things. At this stage, recognising whom in formal texts matters more than producing it yourself; it becomes more useful actively as your writing grows more formal.

Relative clauses built around a preposition

Some relative clauses need a preposition — live in a house, look at a photo, rely on someone. There are two ways to handle it, one more formal than the other:

After a fronted preposition, formal standard English uses which for things and whom for people — ✅ the topic about which we spoke, ✅ the person about whom we spoke, not ❌ the person about who we spoke. You can also front a preposition with whose + noun: ✅ the man to whose house we were invited. Relative that never follows a preposition directly: never ❌ the topic about that we spoke. Everyday English almost always prefers moving the preposition to the end instead, which sidesteps this whole question:

• The colleague with whom I work is moving abroad. → The colleague I work with is moving abroad.
• That's the topic about which we talked. → That's the topic we talked about.

For places, everyday English usually reaches for the relative adverb where rather than in/at which: the city where I was born, the café where we met — a topic in its own right, worth exploring separately.

Common mistakes

• ❌ This is the house which I grew up. → ✅ This is the house which/that I grew up in. / This is the house in which I grew up. (the preposition can't just disappear — it moves to the end, or fronts with which)
• ❌ That's the topic about that we spoke. → ✅ That's the topic about which we spoke. / That's the topic that we spoke about. (relative that never follows a preposition directly)
• ❌ I met a writer who's first novel became a bestseller. → ✅ I met a writer whose first novel became a bestseller. (whose shows possession; who's = who is / who has)
• ❌ The man whom called me is my neighbour. → ✅ The man who called me is my neighbour. (whom is only for the object role, never the subject)
• ❌ That's the man whose his dog barks all night. → ✅ That's the man whose dog barks all night. (whose already carries the possession — no need for his as well)

Quick check

There is more than one right way to complete some of these — the answers cover the everyday option and, where relevant, a more formal one.

1. She's the colleague ____ I share an office with.
2. That's the author ____ latest book just won an award.
3. The city ____ I was born is on the coast.
4. He's the client ____ we're meeting tomorrow.

Key takeaways

• A defining relative clause narrows down which person or thing you mean — no commas, and removing it changes the meaning.
• Whose shows possession (the man whose dog barks) and sits directly before a noun.
• Whom is the formal object form of who — natural in writing and required directly after a preposition, but often replaced by who/that, or dropped, in everyday speech.
• Which, whom, and whose (before its noun) can follow a preposition directly (in which, with whom, to whose house), but that never can as a relative pronoun, and formal standard English uses whom, not who, in that position: not ❌ the house in that I grew up or ❌ the person about who we spoke.
• Everyday English usually prefers moving the preposition to the end of the clause: the house I grew up in over the house in which I grew up.