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While ostensibly a signal to the reader to pause, there is much more to the humble comma than first appears.
While ostensibly a signal to the reader to pause, there is much more to the humble comma than first appears.
Comma - a punctuation mark that separates parts of a sentence so that meaning is clear.
Introduction
Introduction
A comma is generally understood to be a punctuation mark that tells a reader when to pause while reading a sentence.
While this is certainly true, the comma has many other possible uses, from separating list items to identifying non-essential information in a sentence.
Conventional Uses of the Comma
Conventional Uses of the Comma
Titles
Titles
When a person has a title that comes after their name, we should insert a comma before the title.
Examples
The most recognised expert in the field is Jade Wenkins, PhD.
Alan Pierce, MD, will be leading the surgery team.
Direct address
Direct address
When somebody is being addressed directly, that person's name or title should be set off by commas.
Examples
The state of this city is a disgrace, Mayor.
Without you, Susan, we would never have made it through.
Dates
Dates
The use of commas when writing dates differs between British/Australian English and American English.
In British/Australian English the day is written before the month and no commas are required.
Example
The project was completed on 21 November 2022 to great acclaim.
However, if this sentence were recast in American English commas would be required after each element except the month.
Example
The project was completed on November 21, 2022, to great acclaim.
Geographic references
Geographic references
When a sentence includes two or more related geographic elements these elements should be separated by commas.
Examples
Most of the work was completed in Helsinki, Finland.
Los Angeles, California, the United States of America: the place where many go to follow their dreams.
Introductory words or phrases
Introductory words or phrases
When the main clause of a sentence comes after an introductory word or phrase, a comma is used to separate the two.
Incorrect
Yes that is the correct answer to the question.
After dinner they went for a short walk along the beach.
Correct
Yes, that is the correct answer to the question.
After dinner, they went for a short walk along the beach.
Note that the second sentence could be rewritten without the need for a comma.
Example
They went for a short walk along the beach after finishing dinner.
An exception to this is when a sentence with an introductory word or phrase is very short. In this case, no comma is needed.
Unnecessary
Today, I stayed home.
Preferable
Today I stayed home.
Afterthoughts
Afterthoughts
When a final word or phrase comes after the main clause in a sentence, this should be set off with a comma.
Incorrect
Leave the keys on the desk thanks.
You've met my friend haven't you?
I won't be staying around for the reception though.
Incorrect
Leave the keys on the desk, thanks.
You've met my friend, haven't you?
I won't be staying around for the reception, though.
Between Listing Items
Between Listing Items
A comma should be placed after each item in a list; however, it can be tricky to know whether a final comma (the Oxford comma) should be included before the final list item.
Oxford comma (serial comma) - a comma between the final items in a list.
The Australian convention in this case is to omit the Oxford comma, unless confusion arises.
Thus, in simple cases such as the ones below, no Oxford comma is needed.
Examples
Our main courses are beef, chicken and tofu.
"Blood, sweat and tears await us," said the sergeant.
However, note how the Oxford comma is needed in the examples below to avoid confusion.
Confusing
When setting the table, you should place the bowls, glasses and knives and forks.
Most undergraduates take classes in accounting, marketing, microeconomics and macroeconomics.
Preferred
When setting the table, you should place the bowls, glasses, and knives and forks.
Most undergraduates take classes in accounting, marketing, microeconomics, and macroeconomics.
In the first example, knives and forks are considered a single unit in this context, but the repetition of the word and is confusing to the reader without the Oxford comma. In the second example, the Oxford comma makes clear that microeconomics and macroeconomics are separate subjects.
While it is difficult to establish an all-encompassing rule regarding the Oxford comma, it is always best practice to consider how a sentence will be interpreted by the reader. And, when in doubt, read the sentence out loud using each method to see which best communicates the intended meaning.
Setting Off Nonessential Information
Setting Off Nonessential Information
Sometimes, a sentence includes information that is helpful, but not essential, to the main thought being expressed.
A pair of commas should be used to separate this information.
Examples
My new car, which I love, is red.
The report, that Jimmy prepared, helped the company to succeed.
To know whether such a sentence is grammatically correct, we should be able to remove the non-essential information without harming the readability of the sentence.
Examples
My new car is red.
The report helped the company to succeed.
When including nonessential information in a sentence, we should be careful of overburdening the reader.
Example
The comma, which is a punctuation mark, can be misused, and sometimes entirely forgotten, when the care, that is needed, is not taken by the writer.
Note also that nonessential information is often introduced with the words that or which.
Generally, that is used for important information, while which is used for less important information.
In Australian English, the choice between these words is largely a matter of style.
Sentence Types
Sentence Types
In this section, we examine how commas are used in each of the four common sentence types in English.
Compound sentences
Compound sentences
A compound sentence contains two or more independent clauses that are linked by coordinating conjunctions.
In compound sentences, we should place a comma before any coordinating conjunctions.
Incorrect
He came for the coffee but he stayed for the atmosphere.
She had never addressed an audience before yet she quickly got the hang of public speaking and the audience was soon hanging on her every word.
Correct
He came for the coffee, but he stayed for the atmosphere.
She had never addressed an audience before, yet she quickly got the hang of public speaking, and the audience was soon hanging on her every word.
An exception to this is when independent clauses are short and closely connected to one another. In these cases, we don't need to include a comma.
Example
Barry stood for the performance and Bobby sat.
Simple sentences
Simple sentences
Simple sentences contain one independent clause and no dependent clauses. They can, however, contain conjunctions.
While it is tempting to insert a comma before such conjunctions, this is not necessary.
Unnecessary
She bought the phone, but not the cover.
Would you like a single hamburger, or the meal set?
Preferred
She bought the phone but not the cover.
Would you like a single hamburger or the meal set?
An exception to this is when a comma will improve the communication of meaning within a sentence.
Confusing
The car was quick and quickly sold.
Preferred
The car was quick, and quickly sold.
Complex sentences
Complex sentences
Complex sentences contain one independent clause and one or more dependent clauses.
When it comes to complex sentences, the decision to include or omit commas depends on the order of the different clause types.
If a dependent clause comes before the independent clause, a comma should separate the two.
Incorrect
As the sun set the monsters emerged from their caves.
Because it was wet most people stayed in their homes.
Correct
As the sun set, the monsters emerged from their caves.
Because it was wet, most people stayed in their homes.
If the independent clause comes before a dependent clause, a comma is not needed before the dependent clause.
Incorrect
You should try the dessert, if you go there for dinner.
They had to leave, since it was closing time.
Correct
You should try the dessert if you go there for dinner.
They had to leave since it was closing time.
An exception to this is when the dependent clause is not essential to the thought being expressed in the sentence.
Confusing
I always go for a jog in the morning if only for the fresh air.
Preferred
I always go for a jog in the morning, if only for the fresh air.
If two dependent clauses come before the independent clause, a comma is only required after the second dependent clause.
Example
If you pay attention in class and complete all of your homework, your skills will improve.
Compound-complex sentences
Compound-complex sentences
Compound-complex sentences contain two or more independent clauses and at least one dependent clause.
If a sentence begins with a dependent clause that applies to two independent clauses that follow, we should insert a comma after the dependent clause, but not between the two independent clauses.
Example
Because this is such a big project, I will work on administration and you will work on manufacturing.
If a dependent clause occurs between two independent clauses and applies only to the second, we should place a comma before and after the dependent clause.
Example
He prepared the meal too quickly, and when she tasted it, she quickly regretted her decision.
Conflicting rules
Conflicting rules
There are, of course, times when the rules of comma usage clash, or result in strangely-worded sentences.
The Punctuation Guide has an excellent breakdown of how this can occur, and what can be done about it.
In addition, remember that rules are made to be broken. If we feel that a comma is interfering with the meaning of a sentence, we should remove it. And, if we feel that a comma is needed to allow our writing to breathe a little more, we should add one.
As always, the best way to make sure a sentence sounds the way we want it to is to read it out loud: our ears are the best judges.
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