DEFINING clauses (no commas) identify WHICH noun we are referring to — "The report THAT she submitted." NON-DEFINING clauses (with commas) add extra information about something already identified — "The report, WHICH she submitted on Friday, was excellent." In non-defining clauses, THAT cannot replace which/who.
DEFINING RELATIVE CLAUSES: identify or RESTRICT the antecedent (noun) — without the clause, we would not know WHICH of all possible ones we are referring to. NO COMMAS. "The employee who submitted the report has been promoted." If we remove the clause: "The employee has been promoted" = we do not know which employee. RELATIVE PRONOUNS IN DEFINING: WHO (subject people). WHOM (object people, formal). THAT (people or things). WHICH (things/ideas). WHERE (place). WHEN (time). WHOSE (possession). THAT vs WHICH in defining: in informal English, THAT is very common for both people and things. In formal English, WHO is preferred for people and WHICH for things. OMISSION OF PRONOUN: in defining clauses, the relative pronoun CAN be OMITTED when it is the object (not subject): "The report [that] she submitted" = "the report she submitted" = correct. "The employee who submitted the report" = WHO/THAT cannot be omitted because it is the SUBJECT of submitted.
The candidates who have been shortlisted for the final interview stage will be contacted individually by the HR team with the relevant details and scheduling information by the end of this week.
The acquisition strategy that the board approved in Q1 has so far delivered results that are broadly in line with the original financial projections presented at the time of the initial proposal.
Any employee whose performance has been rated as "exceeding expectations" for two consecutive annual review cycles will be automatically considered for inclusion in the accelerated development programme.
NON-DEFINING RELATIVE CLAUSES: add EXTRA, PARENTHETICAL information about the antecedent — which is already sufficiently identified without the clause. WITH COMMAS (function as parentheses). "The CEO, who joined the company in 2019, has announced her resignation." We know who we are talking about (The CEO) without needing the clause — the clause only adds extra information. PRONOUNS IN NON-DEFINING: WHO (people). WHOM (object people, formal). WHICH (things or ideas). WHERE, WHEN, WHOSE = same. CRUCIAL DIFFERENCE: THAT CANNOT BE USED in NON-DEFINING clauses. "The CEO, that joined in 2019, announced her resignation" = INCORRECT. Only WHO/WHICH/WHERE, etc. OMISSION: the pronoun is NEVER omitted in non-defining clauses. "The CEO, joined in 2019, announced her resignation" = INCORRECT. WHICH for the ENTIRE PRECEDING CLAUSE: "She submitted the report on time, which impressed the board" = WHICH refers to everything that precedes, not a specific noun.
The chief financial officer, who has held the role for the past eleven years, has informed the board that he will be stepping down at the end of the current fiscal year to pursue other professional interests.
The new headquarter building, which is located in the financial district and has capacity for approximately two thousand employees, is scheduled to be officially inaugurated in the third quarter of next year.
The proposal was submitted ahead of the original deadline, which meant that the evaluation committee had additional time to conduct a more thorough assessment than had been possible in previous rounds.
Common mistake
THE FOUR MOST FREQUENT ERRORS: (1) USING THAT IN A NON-DEFINING CLAUSE: "The CEO, that joined in 2019, resigned" = INCORRECT. In clauses WITH COMMAS (non-defining): only WHO/WHICH/WHOM/WHERE/WHEN/WHOSE, NEVER THAT. (2) OMITTING THE PRONOUN IN A NON-DEFINING CLAUSE: "The report, she submitted on Friday, was approved" = INCORRECT. In non-defining clauses, the pronoun is NEVER omitted. (3) CONFUSING MEANING BASED ON COMMAS: "The students who failed the exam need extra help" (defining: only those who failed) vs "The students, who failed the exam, need extra help" (non-defining: ALL students failed). Commas fundamentally change meaning. (4) OMITTING COMMAS IN A NON-DEFINING CLAUSE: "The CEO who joined in 2019 has resigned" (no commas = defining, as if there were multiple CEOs). "The CEO, who joined in 2019, has resigned" (with commas = non-defining, there is one CEO and information is added).
Trick to remember it
COMMA TEST: put the clause in parentheses. If the sentence still makes complete sense AND the sentence without the clause clearly identifies the antecedent = NON-DEFINING (with commas). If the sentence without the clause is vague or incomplete = DEFINING (no commas). THAT TEST: in DEFINING clauses, THAT can replace who/which (informal). In NON-DEFINING clauses, THAT is IMPOSSIBLE. = If you cannot use THAT, it is non-defining = use commas. OMISSION TEST: if you can omit the pronoun = DEFINING (pronoun is object). If you CANNOT omit it = DEFINING (pronoun is subject) or NON-DEFINING (pronoun is never omitted in non-defining).
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. "Students who fail need help" (only those who fail). "Students, who all failed, need help" (all failed). Commas = additional info about something already known.
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 cited in linguistics textbooks is: "The children who ate the pie got sick" (defining: only the children who ate the pie got sick — implies some children did not eat the pie) vs "The children, who ate the pie, got sick" (non-defining: all the children ate the pie and all got sick). In spoken English, this distinction is marked by INTONATION (pause before and after the non-defining clause, no pause in defining), but in written English the comma is the only marker. Historically, editors and proofreaders have made catastrophic errors by adding or removing these commas, changing the legal meaning of contracts and wills in some documented cases.
Exercise 1 · Pick the right one
The new data privacy policy, _____ was drafted in close consultation with the company's legal advisors and approved unanimously by the board, will take effect from the first of next month.
Exercise 2 · Pick the right one
All team members _____ have completed the mandatory online training module by the end of this week will receive a certificate of completion to be included in their professional development records.
Exercise 3 · Form the word
NO COMMAS = defining: identifies which one. THAT possible. Pronoun omittable if object. WITH COMMAS = non-defining: adds extra info. THAT impossible. Pronoun never omitted. "Students who fail need help" (only those who fail). "Students, who all failed, need help" (all failed). Commas = additional info about something already known.
THE FOUR MOST FREQUENT ERRORS: (1) USING THAT IN A NON-DEFINING CLAUSE: "The CEO, that joined in 2019, resigned" = INCORRECT. In clauses WITH COMMAS (non-defining): only WHO/WHICH/WHOM/WHERE/WHEN/WHOSE, NEVER THAT. (2) OMITTING THE PRONOUN IN A NON-DEFINING CLAUSE: "The report, she submitted on Friday, was approved" = INCORRECT. In non-defining clauses, the pronoun is NEVER omitted. (3) CONFUSING MEANING BASED ON COMMAS: "The students who failed the exam need extra help" (defining: only those who failed) vs "The students, who failed the exam, need extra help" (non-defining: ALL students failed). Commas fundamentally change meaning. (4) OMITTING COMMAS IN A NON-DEFINING CLAUSE: "The CEO who joined in 2019 has resigned" (no commas = defining, as if there were multiple CEOs). "The CEO, who joined in 2019, has resigned" (with commas = non-defining, there is one CEO and information is added).
COMMA TEST: put the clause in parentheses. If the sentence still makes complete sense AND the sentence without the clause clearly identifies the antecedent = NON-DEFINING (with commas). If the sentence without the clause is vague or incomplete = DEFINING (no commas). THAT TEST: in DEFINING clauses, THAT can replace who/which (informal). In NON-DEFINING clauses, THAT is IMPOSSIBLE. = If you cannot use THAT, it is non-defining = use commas. OMISSION TEST: if you can omit the pronoun = DEFINING (pronoun is object). If you CANNOT omit it = DEFINING (pronoun is subject) or NON-DEFINING (pronoun is never omitted in non-defining).
Bryan López
Founder of SpeakUP Academy