What are the defining relative clauses rules?
Who refers to people, which to things, and that to both in defining clauses. The clause identifies its noun, takes no comma, and allows an object pronoun to be omitted.
- Person: who or that; thing: which or that.
- Defining information takes no comma.
- A relative pronoun used as an object can be omitted.
B1 · Relative Clauses · 10 minDefining relative clauses identify the person or thing you mean.
This B1 lesson shows you how to identify people and things with who, which, and that, avoid commas, and omit object pronouns — free to try, with no signup.
- CEFR levelB1 · Intermediate
- Time to completeAbout 10 minutes
- Core questionWhich person or thing?
- Blocks10 blocks
01 / 06
What are the defining relative clauses rules?
Defining relative clauses identify exactly which person or thing you mean. In "We need a supplier who delivers on time," who delivers on time separates the suitable supplier from all the others. In "We need a system that flags delays," that flags delays performs the same job for a thing. Without that information, the listener does not know which supplier or system is intended. The relative clause therefore belongs closely to the noun and has no comma. The structure combines two ideas without repeating the noun: instead of "We need a supplier. The supplier delivers on time," you create one precise sentence. To choose the pronoun, check person or thing first, then subject or object. The central rule is simple: essential identity stays directly attached to its noun without commas.
02 / 06
What is the who which that difference?
Use who for people, which for things, and that for both in defining relative clauses. A person appears in "the manager who called"; a thing appears in "the system which flags delays." You can also say "the system that flags delays" in the second example. That can refer to a person too, although who makes the personal reference especially clear. German relative forms do not create the same person-versus-thing split, which can produce "The manager which called is from Berlin." Correct it to "The manager who called is from Berlin." Do not follow a translated article or the grammatical gender of the German noun. Check the English reference: person points to who, thing points to which, and that can cover either group in a defining clause.
03 / 06
Do defining relative clauses use a comma?
Defining relative clauses use no comma because they make the reference identifiable. "The report that he sent yesterday contains errors" means that the report sent yesterday is the one with errors. German punctuation requires a comma before every relative clause, which can trigger "The report, that he sent yesterday, contains errors." In English, separating the clause changes its function: commas mark additional, non-defining information and can suggest that only one already identified report is meant. Leave them out for the defining meaning. Before writing, ask whether the clause is needed to know which person or thing is intended. If the answer is yes, keep the information directly beside the noun. The comma decision therefore follows meaning, not the mere presence of a relative pronoun.
04 / 06
When can you omit a relative pronoun?
You can omit the relative pronoun when it is the object in a defining relative clause. Compare "the colleague that you met" with "the colleague you met." In both versions, you is the subject and the colleague is the object of met, so that can disappear. The pattern differs in "the colleague who called." Here who is the subject of called, and removing it would leave no subject; "the colleague called" has a different structure and meaning. Use a simple test. If the relative pronoun is followed by a separate subject such as you, he, or the team, the pronoun is often an object and can be omitted. If a verb follows directly and the pronoun performs the subject role, keep it. Omission then becomes a grammatical decision rather than a stylistic guess.
05 / 06
How do you use defining relative clauses at work?
At work, defining relative clauses make requirements, specifications, and responsibilities precise. "We need a supplier who delivers on time" does not describe any supplier; it establishes a decisive criterion. "We need a system that flags delays" narrows the required function. When referring to a contact, write: "Please ask the colleague you met yesterday." Omitting the object pronoun keeps the sentence concise without losing information. In every example, the relative clause forms part of the identification, so there are no commas. When writing a requirement, identify the noun that needs greater precision, decide whether it is a person or thing, and check whether the pronoun is the subject or object. The fitting form usually follows directly from those checks.
06 / 06
How can you practise defining relative clauses?
Practise English relative pronouns by combining two short sentences into one precise statement. Start with "We chose a supplier. The supplier delivers on time." Replace the repeated noun with who: "We chose a supplier who delivers on time." Repeat the step with a thing and which or that: "We use a system that flags delays." Next mark whether the pronoun is the subject or object. In "the colleague that you met," you can remove it; in "the colleague who called," it must remain. Finally, inspect the commas and remove them when the relative clause identifies the noun. Use examples from requirements, emails, or project descriptions. This trains meaning, form, and punctuation together instead of treating them as three disconnected lists.