ESEN
Which one to use?Intermediateclauseclause
Defining relative clausesvsNon-defining relative clauses
Defining clauses (no commas) identify which noun is meant; non-defining clauses (with commas) add extra information.
Side-by-side comparison
Defining relative clauses
clauseDefining relative clauses (no commas) identify the noun in an essential way. If you remove them, the meaning changes or the sentence loses its point.
The student who scored the highest mark on the test will receive a special prize.
The book that I lent you last week is a signed copy, so please be careful with it.
The café that opened near the school is always full at lunchtime.
Non-defining relative clauses
clauseNon-defining relative clauses (with commas) add extra information about something already identified. You can remove them without changing the main meaning of the sentence.
My sister, who lives in London, is coming to visit us next month.
The new teacher, who started last Monday, has already made a great impression on everyone.
The concert, which lasted over three hours, was absolutely worth the long wait.
Common mistake
- •The most critical error: "The CEO, that joined in 2019, resigned" is wrong, in non-defining clauses (with commas) THAT is impossible; only who/which is allowed.
- •Second: commas change meaning entirely: "Students who failed need help" (only those who failed) vs "Students, who failed, need help" (all of them failed).
Trick to remember it
- •Comma test: can you remove the clause and the sentence still makes complete sense? If yes = non-defining (with commas, no THAT, pronoun mandatory).
- •If removing it leaves the sentence vague = defining (no commas, THAT possible, pronoun omittable if object).
Quick rule
No commas = defining: identifies which one. THAT possible. Pronoun omittable if object. With commas = non-defining: adds extra info. THAT impossible. Pronoun never omitted.
Did you know?
The distinction between defining and non-defining relative clauses is one of the aspects with the greatest PRAGMATIC impact in written English, a comma in the wrong place can completely change the meaning. The classic example in linguistics textbooks: "The children who ate the pie got sick" (defining: only those who ate the pie, implies others did not eat) vs "The children, who ate the pie, got sick" (non-defining: all the children ate the pie and all got sick). In spoken English, the difference is marked by intonation (pause and flatter tone in non-defining clauses), but in writing only the commas distinguish them. Historically, editors have made errors with legal consequences by adding or removing these commas in contracts and wills.
Practise what you learned
Exercise 1 · Pick the right one
The book _____ I recommended is on the bestseller list.
Exercise 2 · Pick the right one
My sister, _____ lives in Paris, is visiting us this weekend.
Exercise 3 · Form the word
Related word pairs
WhatvsWhich
'What' asks from an unlimited set of options; 'which' asks when there is a limited, defined set of options to choose from.
WhichvsWho
'Which' is used for things, animals, and concepts; 'who' is used for people.
WhosevsOf which
'Whose' is the possessive relative for people and things; 'of which' is a more formal alternative for things.
AvsAn
'A' is used before consonant sounds; 'an' is used before vowel sounds.
Bryan López
Founder of SpeakUP Academy