Commas separate parts of a sentence so the meaning is clear. Sentence structure determines their correct use.
Separate introductory words, phrases and clauses with a comma
A comma separates introductory words, phrases and clauses from the main clause of the sentence.
Many introductory phrases can be moved to the end of sentences without changing the meaning. In these cases, you don’t need a comma before the phrase. This simpler structure can be easier to read.
- During the meeting, we discussed Item 9.
- We discussed Item 9 during the meeting.
Place a comma after adverbs and other introductory words
Use a comma after introductory words, such as greetings and adverbs, or when addressing someone. Using an introductory word gives it emphasis.
- Yes, they went to the estimates hearing. [Affirmative emphasis]
- Goodnight, and good luck. [Greeting]
- Actually, that's an interesting point. [Adverb]
- Excuse me, should I come with you? [Addressing someone]
You don’t need a comma after an introductory word if the sentence is very short. This minimises punctuation in very short sentences.
Today I went to work.
Use a comma after phrases and clauses that change the whole sentence
- During the meeting, we discussed item 9. [Adverbial phrase]
- Although they were shaking and sweating, the firefighters were relieved to feel the first drops of a downpour. [Adverbial clause]
Conditional clauses are adverbial clauses (for example, beginning with ‘if’, ‘unless’ or ‘until’). They should also have a comma after them if they start the sentence.
Unless the consultation starts early, it will not finish on time. [A conditional adverbial clause]
Avoid beginning a sentence with a string of numbers and dates
Use a comma after an introductory phrase that ends with a numeral and is immediately followed by another numeral. It doesn’t matter how short the sentence is.
Avoid this type of sentence structure because the string of numbers can be confusing.
There were 16.5 million people enrolled to vote in Australian elections on 18 April 2019.
[This structure avoids stringing a number together with a date.]
On 18 April 2019, 16.5 million people were enrolled to vote in Australian elections.
[This is grammatically correct but less readable.]
Mark out non‐essential information within a sentence
Commas isolate information in a sentence when it isn’t essential to:
- grammatical structure.
Within a sentence, use a pair of commas to separate non-essential or supplementary information. Always check for the second comma where there should be a pair.
Generally, if you can take out part of the sentence and it is still grammatically correct, it should be between a pair of commas.
Check carefully. Using comma pairs can completely change the meaning of a sentence.
The committee, said the secretary, was incompetent. [The committee was incompetent.]
The committee said the secretary was incompetent. [The secretary was incompetent.]
Elements that function as supplementary information include:
- non-essential clauses
- nouns that define the same thing
- question tags.
Set off non-essential clauses
Use commas around clauses that add information but aren’t essential to the meaning of the sentence.
Don’t use commas if the clause is essential for meaning.
If you can remove the clause and your sentence means the same thing, it’s non-essential and should go between commas.
Non-essential clauses are also called ‘non-restrictive’ or ‘non-defining’ clauses.
The business report, which the manager had edited, explained the agency’s strategy.
[The main message is ‘The business report explained the agency’s strategy’. The clause ‘which the manager had edited’ gives more information, adding to the meaning. It doesn’t change the meaning.]
Introduced pests, such as varroa mite, threaten Australian honey production.
[All introduced pests threaten honey production. The varroa mite is just an example.]
The report that the manager had edited explained the agency’s strategy.
[The clause ‘that the manager had edited’ is essential to the meaning because there is no other information in the sentence to identify what report is being referred to.]
Introduced pests from South Asia threaten Australian honey production.
[Only pests from South Asia threaten honey production. Other introduced pests don’t affect honey production.]
Each of these examples separates a grammatical subject from its verb. This is a problem when the subject is overburdened with non-essential information.
Check if you can rephrase the information to make it easier to follow. It is easier for people to read shorter sentences.
The report was tabled last week. It is about demographic changes in rural areas in Western Australia.
The report, detailing demographic changes in rural areas in Western Australia, was tabled last week.
Place commas around nouns that define the same thing they follow
Use a pair of commas when you have 2 noun phrases next to each other that define the same thing.
The strike took place in Whyalla, South Australia, in June 2014.
[The noun phrase ‘South Australia’ is between 2 commas because it is non-essential information. ‘South Australia’ adds to the meaning but doesn’t change the meaning.]
The strike took place in Whyalla, South Australia in June 2014.
You should be able to take out the noun phrase between the comma pair and still have a grammatically correct sentence.
- My colleague, Mx Lesley May, will exercise my proxy vote.
- My colleague will exercise my proxy vote.
The sentence loses detail without the second noun phrase (Mx Lesley May), but it is still a full sentence.
Separate questions tagged onto a sentence
Questions can be tagged onto the end of sentences. Use a comma before a question that is part of the sentence.
- They’re not here, are they?
- We’ll be reporting back, won’t we?
Use commas with the phrase ‘for example’
Generally, use a comma before and after the phrase ‘for example’ in a sentence.
Some colours, for example, are difficult for people with colour blindness to distinguish.
If ‘for example’ begins a sentence, it is an introductory phrase. Follow it with a comma.
For example, some colours are difficult for people with colour blindness to distinguish.
If you’re introducing a bullet list after ‘for example’, use a colon.
Some colours are difficult for people with colour blindness to distinguish, for example:
Don’t use commas with Latin shortened forms
If you use Latin shortened forms, such as ‘e.g.’ and ‘i.e.’, don’t follow them with a comma.
Exports of rare earths (e.g. lithium, europium) have soared.
Exports of rare earths (e.g., lithium and europium) have soared.
Place commas between principal clauses joined together with a conjunction
If they have different subjects, use a comma before the coordinating conjunction.
Do not use this rule to create a sentence of more than 25 words. Shorter sentences are easier to read.
The Senate debated the Bill at length, but the party whips eventually called for a vote.
[‘But’ is the coordinating conjunction. ‘The Senate’ and ‘the party whips’ are each the subjects of a principal clause.]
If 2 clauses share the same subject, you don’t need to repeat the subject or insert a comma before the conjunction.
The company closed its Perth office and sacked the chief financial officer.
[‘The company’ closed an office and sacked an executive officer. ‘The company’ is the subject of both clauses, joined using ‘and’.]
The exception to this rule is when you have joined more than 2 principal clauses with the same subject.
The company closed its Perth office, sacked the chief financial officer, and opened a branch in Singapore.
[The verbs ‘closed’, ‘sacked’ and ‘opened’ each complement the same subject: ‘the company’. Each complement completes a principal clause.]
Don’t use commas to ‘splice’ sentences
Don’t use a comma to link 2 stand-alone sentences unless you use a coordinating conjunction. This kind of error is called a ‘comma splice’.
The report was finished last week, but the minister has not approved its release.
The report was finished last week, the minister has not approved its release.
Punctuate sentence lists and strings of adjectives
Separate items in lists of nouns or adjectives with commas
Use commas between items in a sentence list. Avoid using a comma before the last item in the list.
This rule applies to sentence lists and sentence fragments in bullet lists. Do not punctuate the end of a list item with a comma if it is in a bullet list.
- The delegation visited Brisbane, Canberra and Adelaide.
- The consultation involved businesses, sole traders and not-for-profits.
- The applicant was willing to learn, eager to work and well prepared.
Restrict the use of the Oxford comma
If the last item combines 2 words or phrases with the word ‘and’, use a comma before that final item. This use of the comma is known as the ‘Oxford comma’ or ‘serial comma’.
The industries most affected are retail trade, wholesale trade, and accommodation and food services.
[‘Accommodation and food services’ is listed as a single industry category. It is set off in the list with an Oxford comma.]
The Oxford comma can prevent ambiguity in complex sentence lists. For example, use the Oxford comma before the last item if you’re using a defining phrase applicable only to that final item.
A defining phrase is essential to the meaning of the sentence. The following examples show how the Oxford comma can affect meaning, using the defining phrase ‘for stockfeed’.
The analysis outlined demand for barley, wheat and hay for stockfeed. [All crops are for stockfeed.]
The analysis outlined demand for barley, wheat, and hay for stockfeed. [Only the hay is for stockfeed.]
Separate adjectives of the same type
When writing strings of adjectives, use a set order – evaluative, descriptive, then definitive.
Use commas in strings of adjectives of the same type (for example, a string of descriptive adjectives).
- This is an ethical, profitable, efficient organisation. [Descriptive adjectives]
- They were a happy, caring, devoted workforce. [Evaluative adjectives]
Don’t use commas in strings of adjectives of different types.
- My new black felt-tip pen splattered ink everywhere.
- We found some used French tennis balls left over from a training day.
Use commas in numbers with 4 or more digits
Numbers with 4 or more digits (starting from 1,000) need a comma. Use commas for numerals in text and in tables.
- The total cost of refurbishment was nearly $367,000.
- This budget year will see a surplus of $7.1 billion, equal to 0.4 per cent of GDP.
Don’t use a space between the digits, because screen readers can read them as separate numbers.
The agency handles around 6,500 complaints each year.
The agency handles around 6 500 complaints each year. [This can be read as the number 6 followed by the number 500.]
When you are using numbers of 1,000 or more, use commas to separate the numerals into groups of 3 (working right to left).
Commas are not used to the right of a decimal point.
Don’t use commas in postcodes or dates.
- The year was 2020.
- The office was in postcode area 6500.
Show direct speech or quoted material using commas
Introduce directly quoted speech with a comma. Use the comma in combination with quotation marks.
- She said, ‘It’s time to start work.’
- The Prime Minister said, ‘I’m calling a half-Senate election.’
If an attribution comes after a quotation, use a comma at the end of the quotation and before the quotation mark.
- ‘It’s time to start work,’ she said.
- ‘I’m calling a half-Senate election for Saturday 15 August,’ the Prime Minister said.
If the quotation is broken into 2 parts, the second part should follow a full stop rather than a comma.
- ‘It’s time to start work,’ she said. ‘We have a lot to do.’
- ‘I’m calling a half-Senate election,’ the Prime Minister said. ‘It will be held on Saturday 15 August.’
If the quotation ends the sentence, end it with the original punctuation of the quotation.
- She said, ‘It’s time to start work.’
- She asked, ‘Is it time to start work?’
The digital edition consolidates information from the sixth edition.
It departs from advice in the sixth edition about the position of commas and quotation marks in sentences interrupted by expressions like ‘she said’. The sixth edition recommended the comma be outside the quotation mark. The digital edition recommends the comma be inside the quotation mark.
The Content Guide had brief information about using a comma in sentences and with numbers. It had basic information on using quotation marks. It advised against using Oxford commas.
About this page
Oxford University Press (2016) ‘9.2 Layout of quoted text’, New Oxford style manual, Oxford University Press, Oxford.
University of Chicago (2017) ‘6.40 Commas with quotations’, Chicago manual of style, 17th edn, University of Chicago Press, Chicago.
Dixon JC and Bolitho B (2005–2019) Course notes and exercises: editing and proofreading for the workplace, Centre for Continuing Education, Australian National University, Canberra.
Murphy EM with Cadman H (2014) Effective writing: plain English at work, 2nd edn, Lacuna, Westgate.
Seely J (2001) Oxford everyday grammar, Oxford University Press, Oxford.
Stilman S (2004) Grammatically correct, Writer’s Digest Books, Ohio.
Truss L (2003) Eats, shoots and leaves: the zero tolerance approach to punctuation, Profile Books, London, 2003.