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Comma before "Which" and "Who"
Should I put a comma before "which" and "who"?
"Which" without a comma heads a defining clause, and "which" with a comma heads a non-defining clause. That's the quick answer. We'll return to this.Writers often ask whether they should put a comma before "which" and "who." Unfortunately, the answer isn't quick, but it's simple enough. Before we discuss the grammar, here are two quick workarounds to determine whether the comma is needed. (These also work with "who.")
(Workaround 1) The "That" Test.
If you can replace your "which" with "that," don't use commas with your "which."
- The fruit which I bought on Tuesday has turned rotten. (I'm still undecided whether I need commas at this point.)
- The fruit that I bought on Tuesday has turned rotten.
- The fruit which I bought on Tuesday has turned rotten.
- Dexter which I've had for two years can now open the fridge. (I'm still undecided whether I need commas at this point.)
- Dexter that I've had for two years can now open the fridge.
- Dexter, which I've had for two years, can now open the fridge.
If you'd happily put parentheses (round brackets) around the "which" clause or even delete it, then offset it with commas.
- Step 1: Find the clause starting with "which."
- My car which I bought only last week won't start. (I'm still undecided whether I need commas at this point.)
- Step 2: Put the clause in parentheses or even delete it.
- My car (which I bought only last week) won't start.
- My car
which I bought only last weekwon't start.
(Yes, it still makes sense if I delete it.)
- My car, which I bought only last week, won't start.
- Step 1: Find the clause starting with "which."
- The fruit which I bought on Tuesday has turned rotten. (I'm still undecided whether I need commas at this point.)
- Step 2: Put the clause in parentheses or even delete it.
- The fruit (which I bought on Tuesday) has turned rotten.
- The fruit
which I bought on Tuesdayhas turned rotten.
(I'm not happy with this because not all of my fruit has turned rotten.)
- The fruit which I bought on Tuesday has turned rotten.
More on Using a Comma before "Which" and "Who"
Let's do the grammar.If the information provided by the clause introduced by "who" or "which" is necessary to define the person or thing it is describing (i.e., it's not just some extra information you could easily remove), then the clause is not offset with commas.
- The car which hit the snowdrift is a write-off.
- The car that hit the snowdrift is a write-off.

Rule on Using Commas with "Which" and "Who"
Here is the rule:More Examples of Commas with "Which" and "Who" Clauses
Here are some more examples with "who" clauses:- The boy who broke our window brought some flowers to the door.
- The driver who stole indicator bulbs for his own car was given a formal warning.
- Jeremy Buxton of 16 High Street who was born in Boston is the second person from the village to represent the country at basketball.
- Sarah has always been close to her parents who live in the same village as us.


- her parents who live in the same village
- her parents who live somewhere else
Real-life Examples
Here are some real-life examples of clauses that are required to define. (Remember that these are called restrictive clauses or defining clauses.)- The man who doesn't read good books has no advantage over the man who can't read them.
(Author Mark Twain)
- It is only shallow people who do not judge by appearances.
(Playwright Oscar Wilde)
- The man who can dominate a London dinner-table can dominate the world.
(Playwright Oscar Wilde)
- One should never trust a woman who tells one her real age. A woman who would tell one that would tell one anything.
(Playwright Oscar Wilde)
More Examples of "Which" and "Who" Clauses with Commas
Remember that if the information provided by the "who" and "which" clause is just additional information (i.e., it is not required to define the word it is modifying), then it must be separated from the rest of the sentence with commas.In other words, if you'd happily put brackets around it or delete it, then you must at least put commas around it. (These are called non-restrictive clauses or non-defining clauses.)
Examples:
- His youngest daughter, who was born on 16 June 1972, was selected for astronaut training.
- James Baker's cat made its own way home after it was accidentally left on the beach at Scarborough. James, who has lived in our village for 10 years, has just won the lottery.
- William Scott is a millionaire. William who bought his first house in the '80s is estimated to be worth more than 10 million pounds.
"Which" or "That"?
Using "which" without a comma (i.e., for a restrictive clause) is an unpopular practice, especially in the US. Here is an example of "which" without a comma:- Experience is a comb which nature gives us when we are bald. (well-known proverb from Belgium)
More about "That" with a Restrictive Clause
When a clause is necessary for defining (or identification), it is called a restrictive clause. It is described as "restrictive" because it restricts the meaning of the word it modifies. It is also called a "defining clause," which, I think, is a more accurate term. There are never commas around a restrictive clause. When introducing a restrictive clause, the words "who" and "which" can be replaced with "that." (NB: There are never commas around a clause which starts with "that.")Here is an example with "who":
- The boy who broke our window bought me some flowers.
- The boy that broke our window bought me some flowers.
- The PC which keeps breaking down is under guarantee.
- The PC that keeps breaking down is under guarantee.
- The reprimand which you received was justified.
- The reprimand that you received was justified.
- The reprimand you received was justified.
Commas Are Being Used as Parenthetical Punctuation
With a non-restrictive clause, you could equally use parentheses (round brackets) or dashes instead of commas. These are all types of parenthetical punctuation.- Manx cats, which live on the Isle of Man, have a longer life expectancy than normal domestic cats.
- Manx cats (which live on the Isle of Man) have a longer life expectancy than normal domestic cats.
- Manx cats – which live on the Isle of Man – have a longer life expectancy than normal domestic cats.
- Manx cats have a longer life expectancy than normal domestic cats.
Beware of Ambiguity
Look at the sentences below. Both are grammatically correct, but they have different meanings.- Manx cats, which live on the Isle of Man, have a longer life expectancy than normal domestic cats.
- Manx cats which live on the Isle of Man have a longer life expectancy than normal domestic cats.
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