A comma is one of four punctuation marks, any of which cause a reader to pause.
The comma is the lightest punctuation mark. It is a slight steer to the reader to pause. It can be used to break a sentence into more meaningful parts.
Commas can be used singly, to break up a sentence, or in pairs to isolate text which needs to be taken in separately by the reader. Here are 20 ways to use a comma:
AT THE START OF A SENTENCE
#1 Use a comma when beginning sentences with introductory words such as well, now, or yes.
Yes, I do need you to clean your bedroom right now.
Well, I never thought your mother liked me.
#2 Use a comma after phrases of three or more words.
To apply for this post, you must have teaching experience.
On 14 March, we are to be wed.
#3 When starting a sentence with a weak clause, use a comma after it.
If you are not sure where to go, let me know now.
DO NOT use a comma when the sentence starts with a strong clause followed by a weak clause:
Let me know now if you are not sure where to go.
[A strong clause is one which could stand as a sentence (eg Let me know now); a weak clause will not.]
COMMAS IN CONJOINED SENTENCES
#4 Use a comma to separate two strong clauses joined by a coordinating conjunction (and, or, but, for, nor).
I have cleaned the whole house, but she is still working her way through the ironing mountain.
The comma is not needed if both clauses are short:
I cleaned and she ironed.
#5 Use the comma to separate two sentences if it will help to avoid confusion.
I chose the vegetables, carrots and cauliflower, and cauliflower was his preferred choice.
COMMAS MID SENTENCE
#6 Use commas surrounding interrupters such as therefore and however.
I would, therefore, like you to behave.
I would be happy, however, to lend you five pounds.
#7 Use commas to set off ‘asides’ that interrupt the flow of the sentence.
I am, as you will have already guessed, several months pregnant!
#8 Use a comma for non-essential information.
Frances, who works in Accounts, was in an auto accident.
Here the description is essential so commas are not used:
The lady who works in Accounts was in an auto accident.
AT THE END OF A SENTENCE
#9 Use a comma to separate a statement from a question.
I can stay if I want to, can’t I?
#10 Use a comma to separate contrasting parts of a sentence.
That is my decision, not yours.
#11 Use either a comma (or a semicolon) before introductory words (such as namely, that is, i.e., for example, e.g., or for instance) when they are followed by a series of items.
Use a comma also, after the introductory word.
You may be inclined to buy many items of equipment, e.g., pots, pans, and cutlery.
[The comma after ‘pans’ is called the Oxford comma. Whether you include it is a matter of style, rather than grammar.]
COMMAS WITH PROPER NOUNS, TITLES, DATES, ADDRESSES
#12 Use commas before or surrounding the name or title of a person directly addressed.
Will you, Stephen, pass the salt for me?
Yes, Mummy, I will.
#13 Use commas to surround degrees or titles used with names.
Jo Brown, MD, chaired the meeting.
#14 Use a comma to separate the day of the month from the year and after the year.
We met on December 15, 2003, in Ripley.
If any part of the date is omitted, or the date is rearranged (day, month, year), leave out the comma:
We met in December 2003 in Ripley.
We met on 15 December 2003 in Ripley.
#15 Use a comma to separate the town/city from the county.
I live in Salcombe, Devon.
[On envelopes to be sent via snail mail, do not use any punctuation.]
COMMAS WITH ADJECTIVES
#16 Use a comma to replace ‘and’ between two adjectives.
She is a strong, intelligent woman.
You would not say expensive and seaside resort, so no comma here.
We honeymooned at an expensive seaside resort.
#17 Use a comma when an -ly adjective is used with other adjectives.
Frances is a lonely, young girl.
Here: Brightly is not an adjective; brightly lit is. Therefore, no comma is used between brightly and lit.
I get a migraine in brightly lit rooms.
COMMAS WITH VERBS
#18 If the subject is omitted for the second verb, do not use a comma.
He looked as if he knew but still did not answer correctly.
He looked as if he knew, but still he did not answer correctly.
COMMAS IN LISTS
#19 To avoid confusion, separate words and word groups with a series of three or more.
My £50 million estate is to be split among my wife, son, daughter, and sister.
Omitting the comma after daughter (yes, it’s another Oxford comma) would imply that the daughter and sister would have to split one-third of the estate.
COMMAS IN DIALOGUE
#20 Use commas to introduce or interrupt direct quotations.
Gail said, “I really do not care.”
“Why,” Dad shouted up the stairs, “do you always forget to do it?”