Relative Clauses: Who/Which/That + Commas (The Clean Rules)

A practical guide to defining vs non-defining clauses, comma use, and quick edits that make your writing clearer instantly.

Here’s the topic in a compact form you can screenshot and revise quickly.

| # | Decision rule | |---:|---| | 1 | Defining clauses identify which noun you mean; non-defining clauses add extra info and need commas. | | 2 | Use who for people, which for things; that often appears in defining clauses. | | 3 | If removing the clause changes the identity, it’s defining (usually no commas). | | 4 | Rewrite drill: remove the clause; check meaning; then decide commas/pronoun. | | 5 | In exams, punctuation is a scoring lever—clean commas improve readability. |

English grammar feels simple until you have to write clearly under time pressure. The trick is to learn **decision rules** (what to choose and when) rather than memorizing a long list of terms. Good grammar is readable grammar: the reader never has to re-check the subject, the time, or the logic. (See our English B2/C1 chapters for hedging and cautious language, cleft sentences and inversion for emphasis, advanced and mixed conditionals, articles in context, and workplace collocations.) German speakers: focus on articles, prepositions, and continuous aspect. Hindi speakers: focus on subject-verb agreement, article presence, and phrasal verbs. If you’re studying for an exam, your goal is not “perfect grammar,” it’s **predictable grammar**: structures you can use reliably. A shorter sentence with clean grammar scores better than a long sentence full of risky clauses. At B2/C1 the examiners reward controlled complexity—hedging, clear connectors, and consistent tense—more than flashy vocabulary alone.

Defining clauses identify which noun you mean; non-defining clauses add extra info and need commas. The key is to identify the **signal** in a sentence and apply the rule automatically, without overthinking.