The meaning changes greatly depending on whether commas are used (nonrestrictive use) or not used (restrictive use). Let us make sure we understand this difference.
Basic Rules
Restrictive use (no commas): Identifies or limits the antecedent.
“I have a friend who lives in Tokyo.”
Nonrestrictive use (with commas): Adds supplementary information about the antecedent.
“I have a friend, who lives in Tokyo.”
In nonrestrictive use, that cannot be used (only which/who/whom/whose).
In nonrestrictive use, which can refer to the preceding clause or the whole sentence as its antecedent: “He passed the exam, which surprised everyone.”
Students who study hard will succeed. ← Restrictive use
My sister, who lives in London, is a doctor. ← Nonrestrictive use
He was late again, which made his boss angry. ← which refers to the whole clause
Points to Note
① that cannot be used in nonrestrictive use: “× My sister, that lives in London, ...” is incorrect.
② When the antecedent is a proper noun or person's name: Since it is already identified, the nonrestrictive use is almost always used.
③ When , which refers to the whole clause: It is important to determine exactly what the antecedent of “, which” is.
- No commas (restrictive): identifies or limits the antecedent
- With commas (nonrestrictive): adds supplementary information about the antecedent
- that cannot be used in nonrestrictive use
- , which can refer to the preceding clause or the whole sentence as its antecedent
Practice
- Explain the difference in meaning between the following two sentences: (a) I have a brother who is a doctor. (b) I have a brother, who is a doctor.
- Translate the following into English: She won the first prize, which made her parents very proud.
- Correct the error: My father, that worked as a teacher, retired last year.