“Which” is a relative pronoun used to introduce a relative clause. Whether you need a comma before “which” depends on which kind of relative clause it introduces:
You need a comma before “which” when it introduces a nonrestrictive clause: a clause providing extra information that isn’t essential to the sentence’s meaning.
There’s no comma before “which“ when it introduces a restrictive clause: a clause that couldn’t be removed without changing the sentence’s meaning.
Examples of when to use a comma before “which”
“Which” introducing a nonrestrictive clause (comma)
“Which” introducing a restrictive clause (no comma)
My car, which is a blue Ford Focus, was stolen last week.
The car which was reported stolen was a blue Ford Focus.
I can’t wait for Christmas, which is my favourite holiday.
The subjects which I struggle most with are chemistry and history.
TipThe easiest way to check whether a comma is needed is to see what the sentence looks like without the “which” clause:
If it still expresses the same meaning (e.g., “My car was stolen last week”), you need the comma.
If it means something less specific (e.g., “The car was a blue Ford Focus”; what car?), no comma is needed.
Published on
21 March 2023
by
Jack Caulfield.
Revised on
26 October 2023.
The prepositional phrase “such as” is used to introduce examples or to specify something about the phrase it modifies.
There’s a comma before “such as” when it introduces examples that could be left out.
There’s no comma before “such as” when it introduces essential identifying information
Examples of when to use a comma before “such as”
“Such as” introducing examples (comma)
“Such as” introducing identifying information (no comma)
Many types of animals, such as fish and seabirds, live in marine environments.
Animals such as dogs and cats make good household pets.
The book touches on a number of complicated topics, such as music theory, brain chemistry, and artificial intelligence.
I enjoy learning about topics such as history and technology.
TipTry a simple trick to confirm whether you need a comma: remove the “such as” phrase. If the sentence still expresses the same basic meaning, add the comma. If not, no comma is needed.
“The book covers a number of complicated topics” expresses the same point as the original sentence, but “I enjoy learning about topics” is so vague that it’s not really expressing any clear point. The “such as” clause is essential in the latter sentence, so there’s no comma.
When using the conjunction ‘so’ to connect two clauses, you can tell whether to add a comma before it with a simple trick:
When ‘so’ could be replaced with ‘therefore’, use a comma before ‘so’.
When ‘so’ could be replaced by ‘so that’, don’t add a comma.
Examples of when to use a comma before ‘so’
‘So’ meaning ‘therefore’ (comma)
‘So’ meaning ‘so that’ (no comma)
I was hungry, so I ate some chips.
Maria is saving up so she can move out.
I was hungry. Therefore, I ate some chips.
Maria is saving up so that she can move out.
Note‘So’ also has a variety of other uses in which it isn’t classed as a conjunction but instead as an adverb or another part of speech. In these uses, there’s generally no comma needed (e.g., ‘I think so‘, ‘there’s only so much time’, ‘say it’s not so‘).
The serial comma (aka Oxford comma or Harvard comma) is a term that describes the use of a comma before the conjunction in a list of three or more items (e.g., the comma before ‘and’ in ‘pancakes, scrambled eggs, and bacon’). The name comes from the fact that it’s used in a series (list).
The serial comma is optional – it’s not an error to leave it out or to include it. Different style guides and publishers have different recommendations, but academic style guides normally recommend using it.
If you need to follow a particular style, check out our quick summary of who recommends the serial comma below. If you don’t, the choice is up to you. Just write according to your own preference.
The word ‘while’ has a couple of different meanings. Depending on which meaning you intend, you may or may not need a comma before ‘while’.
If you’re using ‘while’ to mean ‘during the time that’, you don’t need a comma.
Example: ‘While’ meaning ‘during the time that’Please don’t distract me while I’m working.
If you’re using ‘while’ to mean ‘although’ or ‘whereas’, you need a comma.
Example: ‘While’ meaning ‘whereas’Some people enjoy travelling,while others prefer to stay home.NoteSimilar rules apply to other subordinating conjunctions: commas before ‘because’ and commas before ‘as well as’.
Published on
7 March 2023
by
Jack Caulfield.
Revised on
11 September 2023.
You normally shouldn’t use a comma before ‘because’ when the reason that ‘because’ introduces is essential to your meaning. For example, the point of the sentence below is to give a reason for good grammar’s importance.
Examples: ‘Because’ introducing essential clauseGood grammar is important because it allows you to express yourself clearly.
When you add a comma before ‘because’, it removes the emphasis from the reason it introduces. The main point of the sentence below is simply to state the importance of good grammar; the reason is an afterthought.
Examples: Comma before ‘because’Good grammar is important, because it allows you to express yourself clearly.NoteSimilar rules apply to other subordinating conjunctions: commas before ‘while’ and commas before ‘as well as’.
Published on
7 March 2023
by
Jack Caulfield.
Revised on
11 December 2023.
The Oxford comma (also known as the serial comma or Harvard comma) is the use of a comma before the conjunction in a list of three or more items (e.g., the comma before ‘and’ in ‘paints, brushes, and canvas’). The name comes from the fact that it’s recommended by Oxford University Press.
The Oxford comma is optional – it’s not a grammatical error to leave it out or to include it. Different style guides and publishers have different recommendations about its use, though major style guides recommend using it more often than not.
If you need to follow a particular style guide, check out our quick summary of who recommends the Oxford comma below. If you don’t, the choice is up to you; just write according to your own preference.
