Relative Clauses Overview

A relative clause is part of a sentence that gives more information about a noun. It begins with a relative pronoun such as who, which, that, whose, where, or when, and lets you join two ideas into one sentence. For example, instead of I know a man. He speaks Japanese, you can say I know a man who speaks Japanese. Relative clauses come in two types — defining (essential information) and non-defining (extra information) — and learning to use them makes your sentences longer, smoother, and more natural.

A defining relative clause gives essential information that identifies which person or thing you mean: The woman who lives next door is a nurse. Without it, you would not know which woman. A non-defining clause gives extra, non-essential information: My sister, who lives in Spain, is visiting. The sentence still makes sense without it. The two key differences are punctuation and the use of that: defining clauses have no commas and can use that; non-defining clauses need commas and cannot use that.

You can use that only in defining relative clauses, where it can replace who (for people) or which (for things): the bus that goes to town or the man that I met. In non-defining clauses — the kind with commas — that is not allowed; you must use who, which, or whose: My car, which is ten years old, still runs well (not my car, that is ten years old). Remembering that that never follows a comma is a reliable rule.

You can omit the relative pronoun (who, which, or that) only in defining clauses, and only when it is the object of the clause — that is, when another subject and verb follow it: The film (that) we watched was great. Here we is the subject, so that can be dropped. You cannot omit the pronoun when it is the subject of the clause: The man who lives here needs who, because there is no other subject. A quick test: if a noun or pronoun comes right after the relative pronoun, you can usually leave it out.

Use commas only with non-defining relative clauses — the ones that add extra, non-essential information: The Eiffel Tower, which was built in 1889, is in Paris. The commas act like brackets, showing that the clause could be removed without losing essential meaning. Do not use commas with defining clauses, which identify the noun: The tower that we visited was closed. A useful test: if you can remove the clause and the sentence still tells you exactly which thing is meant, use commas; if removing it leaves the noun unclear, do not.

Use who for people and which for things and animals. For example: the teacher who helped me (a person) but the car which broke down (a thing). In defining clauses, that can replace either: the teacher that helped me or the car that broke down. A common error is using which for people (the man which I met is wrong) — always use who or that for people. For possession, use whose with both people and things: the writer whose book I read.

Whose shows possession and connects a noun to its owner. It works with both people and things: the man whose car was stolen or a company whose profits are rising. It is followed directly by a noun (the thing possessed), with no article in between: the student whose essay won — not the student whose the essay won. Learners often confuse whose with who's (a contraction of who is), but in a relative clause showing possession, the correct word is always whose.

Use where to refer to a place and when to refer to a time. For example: the town where I grew up and the year when we met. These are convenient alternatives to a preposition plus which: the town where I grew up means the same as the town in which I grew up, but is more natural in everyday English. With when, you can often omit it in defining clauses: the day (when) we arrived. Both where and when can appear in defining and non-defining clauses.

Yes. A special non-defining use of which can refer back to an entire clause or idea, not just a single noun: He passed all his exams, which delighted his parents. Here which refers to the whole fact that he passed. This structure always needs a comma and always uses which (never that or what). It is useful for adding a comment or reaction at the end of a sentence. Be careful not to overuse it, and make sure the meaning of which is clear from the preceding clause.

In The man who I met was kind, the pronoun who is the object of the clause (I met the man), so it can be dropped: The man I met was kind. Both versions are correct in a defining clause. The shorter form without the pronoun is extremely common in spoken and written English. Note that in very formal English the object form whom is also possible (the man whom I met), but in everyday usage either who or no pronoun at all is more natural. You can never drop the pronoun if it is the subject.