Relative clauses 1: Clauses with who/that/which

Relative clauses give extra information about a noun (the antecedent). We use pronouns like who, that, and which to introduce these clauses. They can define or add non-essential information about people, things, or groups.

• Who = refers to people (e.g., the employee who manages the team).
• Which = refers to things or animals (e.g., the device which arrived yesterday).
• That = can refer to people or things in defining (restrictive) clauses (e.g., the policy that affects us).
• Remember the difference between restrictive (no commas) and non-restrictive (with commas) clauses.

Follow these simple rules when deciding which pronoun to use:

• Use who for people: The employee who submitted the form.
• Use which for things in non-restrictive clauses (with commas): The server, which is new, is faster.
• Use that for essential (restrictive) clauses without commas: The policy that applies to remote workers.
• Avoid using that in non-restrictive clauses (with commas).

If you add commas around the clause, use which (not that); if you don't use commas, that is often the preferred choice for defining clauses.

Avoid these frequent errors when using relative clauses:

• Using 'that' with commas in a non-restrictive clause (wrong): The office, that is new, is busy.
• Using 'which' for people or 'who' for things (wrong categories).
• Omitting the relative pronoun when it is required: The report you sent is late. (ok if object omitted) — but be careful with subject positions.
• Confusing subject vs object in the clause (who vs whom) and then using incorrect word order.
• Incorrect punctuation: leaving out commas for non-restrictive clauses or adding them to restrictive ones.

Check whether the clause is essential to identify the noun (restrictive) or just adds extra info (non-restrictive).