Rules for comma usage
Comma with Subjects and Verbs
With few exceptions, a comma should not separate a subject from its verb.
Writers are often tempted to insert a comma between a subject and verb this way because speakers sometimes pause at that point in a sentence. But in writing, the comma only makes the sentence seem stilted.
Be especially careful with long or complex subjects:
Comma Between Two Nouns in a Compound Subject or Object
Don’t separate two nouns that appear together as a compound subject or compound object.
When a subject or object is made up of two items and the second item is parenthetical, you can set off the second item with commas—one before it and one after it. But you don’t need a comma when you’re simply listing two items.
Comma Between Two Verbs in a Compound Predicate
You get a compound predicate when the subject of a sentence is doing more than one thing. In a compound predicate that contains two verbs, don’t separate them with a comma.
This mistake is most common when the predicate is made up of long verb phrases.
Don’t use a comma in compound predicates unless there is a chance of misreading:
In the sentence above, you need the comma to make clear that it was Cleo who waved, not the man.
When you want to join two independent clauses, you need a conjunction or a semicolon. A comma alone isn’t strong enough to join them. This kind of mistake is called a comma splice.
You can fix a comma splice by adding a conjunction or changing the comma to a semicolon.
Or, you can simply write the two independent clauses as separate sentences.
Comma After Introductory Phrase
A comma normally follows participial phrases that introduce a sentence:
When an adverbial phrase begins a sentence, it’s often followed by a comma but it doesn’t have to be, especially if it’s short. As a rule of thumb, if the phrase is longer than about four words, use the comma. You can also use a comma with a shorter phrase when you want to emphasize it or add a pause for literary effect.
But, if there is a chance of misreading the sentence, use the comma:
Comma Within a Comparison
Don’t use a comma before “than” when you’re making a comparison.
Commas with Interrupters or Parenthetical Elements
Interrupters are little thoughts that pop up in the middle of a sentence to show emotion, tone, or emphasis. A parenthetical element is a phrase that adds extra information to the sentence but could be removed without changing the meaning of the sentence. Both interrupters and parenthetical elements should be set off with commas.
Comma with a Question Tag
A question tag is a short phrase or even a single word that is added to the end of a statement to turn it into a question. Writers often use question tags to encourage readers to agree with them. A question tag should be preceded by a comma.
Comma with Direct Address
When addressing another person by name, set off the name with commas.
Comma with an Appositive
An appositive is a word or phrase that refers to the same thing as another noun in the same sentence. Often, the appositive provides additional information about the noun or helps to distinguish it in some way. If you could remove the appositive without changing the meaning of the sentence, it is said to be nonessential and should be set off with commas. If the appositive is necessary, it’s said to be essential and it should not be set off with commas.
Commas in Dates
When writing a date in month-day-year format, set off the year with commas.
If you are using the day-month-year format, however, commas are unnecessary.
If you are referencing a day of the week and a date, use a comma:
When you are referencing only a month and year, you don’t need a comma.
Comma Between Coordinate Adjectives
When multiple adjectives modify a noun to an equal degree, they are said to be coordinate and should be separated by commas. One way to tell whether the adjectives are coordinate is to try switching the order of them. If the sentence still sounds natural, the adjectives are coordinate.
If the adjectives are not coordinate, don’t separate them with a comma.
Comma Before But
Use a comma before the word but if it is joining two independent clauses:
If but is not joining two independent clauses, leave the comma out.
Comma Before And
When you have a list that contains only two items, don’t use a comma before the and.
When correcting a comma splice, that is when joining two independent clauses with a coordinating conjunction, put the comma before and.
Commas with Lists
When you have a list that contains more than two elements, use commas to separate them.
(The comma before the and in a list of three or more items is optional. See below under Serial Comma for more information.)
Your list might be made up of nouns, as in the example above, but it could also be made up of verbs, adjectives, or clauses. Imagine, for a moment, that you have just finished doing three chores. The chores were:
- Cleaning the house and garage
- Raking the lawn
- Taking out the garbage
If you were to list these three chores in a sentence, you would write:
Serial Comma (Oxford Comma)
As mentioned above, when you are listing three or more items, commas should separate each element of the list. However, the final comma—the one that comes before the and—is optional. This comma is called the serial comma or the Oxford comma.
Whether or not you use the serial comma is a style choice. Many newspapers do not use it. Many trade books do use it. In your own writing, you can decide for yourself whether to use it or not—just be consistent.
Keep in mind, though, that occasionally the serial comma is necessary for clarity.
The sentence above will almost certainly cause readers to do a double-take. Without a serial comma, it looks like “Jane Austen and Albert Einstein” is an appositive, rather than two more elements in a list. To put it another way, the writer seems to be saying that her parents are Jane Austen and Albert Einstein. A serial comma eliminates the possibility of misreading, so even if you’re not using serial commas in your writing, make an exception for sentences like this:
Comma Separating a Verb and Its Object
Don’t separate a transitive verb from its direct object with a comma.
Comma with Nonrestrictive Clause
A nonrestrictive clause offers extra information about something you have mentioned in a sentence, but the information isn’t essential to identify the thing you’re talking about. Nonrestrictive clauses are usually introduced by which or who and should be set off by commas.
The clause “which Chester recommended” is nonrestrictive because “Posey’s Cafe” is already specific. Identifying it as the restaurant recommended by Chester doesn’t narrow it down any further.
The clause “whom I love dearly” is nonrestrictive because you could remove it and it would still be clear that you’re talking about the same person—“my wife” is already specific.
Comma with Restrictive Clauses
A restrictive clause adds necessary information about something you have mentioned in a sentence. Restrictive clauses are often introduced by that or who and should never be set off by commas.
The clause “that Chester recommended” is essential information in the sentence above. If you removed it, there would be no way to tell which restaurant you were talking about.
Comma Between Correlative Conjunctions
Correlative conjunctions are conjunctions that come in pairs (such as either/or, neither/nor, and not only/but also) and connect words or phrases in a sentence to form a complete thought. Typically, commas are unnecessary with correlative conjunctions.
Comma Between Direct Quote and Attributive Tag
An attributive tag is a phrase like “he said” or “she claimed” that identifies the speaker of a quote or piece of dialogue. Attributive tags can come before, after, or even in the middle of a quote. Use commas to separate attributive tags from quotations.
If a quotation before an attributive tag ends in a question mark or exclamation point, however, there’s no need for a comma.
Comma Inside Quotation Marks
In American English, commas always go before closing quotation marks.
In British English, however, unquoted punctuation typically follows the quotation marks. If you are writing for a British audience, put the comma after the closing quotation mark. Furthermore, British English tends to use single quotes rather than double quotation marks.
Comma Before Parenthesis
Parentheses are used to give additional information to the reader—information that would disrupt the flow of the sentence if written as a nonrestrictive clause. Commas may be placed after the closing parenthesis but not before either the opening or the closing parenthesis. If the sentence would not require any commas if the parenthetical statement were removed, the sentence should not have any commas when the parentheses are added.
Comma Between an Article and Noun
Don’t use a comma between an article and a noun.
When speaking, we often pause while we think of the next word we want to say. In writing, though, there’s usually no reason to add this pause. If you’re writing dialogue and you specifically want to convey a pause here while someone is thinking, use an an ellipsis: I’ll have an… apple.
Comma with As Well As
The phrase “as well as” usually doesn’t require commas unless it’s part of a nonrestrictive clause.
Comma with Such As
The phrase “such as” requires commas if it introduces a nonrestrictive clause.
If “such as” introduces a restrictive clause, omit the commas.
Comma Before Too
Using a comma before “too” is optional.
A comma simply adds emphasis.