Rules of Thumb
Comma usage errors fall into two categories: using unnecessary commas and failing to use necessary commas. To avoid making errors when using commas in your writing, you must understand when commas belong (and when they don't).
Keep the following rules of thumb in mind for when to not use commas.
Do not use a comma to separate a subject from its predicate.
- Incorrect: Registering for our fitness programs before September 15, will save you thirty percent of the membership cost.
- Correct: Registering for our fitness programs before September 15 will save you thirty percent of the membership cost.
Do not use a comma to separate a verb from its object, or a preposition from its object.
- Incorrect: I hope to mail to you before Christmas, a current snapshot of my dog Benji.
- Incorrect: She traveled around the world with, a small backpack, a bedroll, a pup tent, and a camera.
- Correct: I hope to mail to you before Christmas a current snapshot of my dog Benji.
- Correct: She traveled around the world with a small backpack, a bedroll, a pup tent, and a camera.
Do not misuse a comma after a coordinating conjunction.
- Incorrect: Sleet fell heavily on the tin roof but, the family was used to the noise and paid it no attention.
- Correct: Sleet fell heavily on the tin roof, but the family was used to the noise and paid it no attention.
Do not use commas to introduce restrictive (i.e., necessary) modifiers.
- Incorrect: The fingers, on his left hand, are bigger than those on his right.
- Correct: The fingers on his left hand are bigger than those on his right.
Do not use a comma before a dependent clause that comes after an independent clause. This is called a disruptive comma.
- Incorrect: The future of print newspapers appears uncertain, due to rising production costs and the increasing popularity of online news sources.
- Incorrect: Some argue that print newspapers will never disappear, because of their many readers.
- Correct: The future of print newspapers appears uncertain due to rising production costs and the increasing popularity of online news sources.
- Correct: Some argue that print newspapers will never disappear because of their many readers.
Do not use a comma after a short introductory prepositional phrase unless you mean to add extra emphasis.
- Incorrect: Before the parade, I want to eat pizza.
- Correct: Before the parade I want to eat pizza.
Do not use a comma between adjectives that work together to modify a noun.
- Incorrect: I like your dancing, cat t-shirt.
- Correct: I like your dancing cat t-shirt.
Do not use a comma to set off quotations that occupy a subordinate position in a sentence, often signaled by the words "that," "which," or "because."
- Incorrect: Participating in a democracy takes a strong stomach because, "it requires a certain relish for confusion," writes Molly Ivins.
- Correct: Participating in a democracy takes a strong stomach because "it requires a certain relish for confusion," writes Molly Ivins.
Do not use a comma when naming only a month and a year.
- Incorrect: The next presidential election will take place in November, 2016.
- Correct: The next presidential election will take place in November 2016.
Do not use a comma in street addresses or page numbers, or before a ZIP or other postal code.
- Correct: The table appears on page 1397.
- Correct: The fire occurred at 5509 Avenida Valencia.
- Correct: Write to the program advisor at 645 5th Street, Minerton, Indiana 55555.
Comma Splice Errors
A comma splice occurs when two independent clauses (that is, two complete sentences) are joined only by a comma. In those situations, an acceptable form of punctuation would be a semicolon or a period. For example:
- Incorrect: Every day, millions of children go to daycare with millions of other kids, there is no guarantee that none of them are harboring infectious conditions.
- Incorrect: Many daycares have strict rules about sick children needing to stay away until they are no longer infectious, enforcing those rules can be very difficult.
- Incorrect: Daycare providers often undergo extreme pressure to accept a sick child "just this once," the parent has no other care options and cannot miss work.
Once you discover where the two independent clauses are "spliced," there are several ways to separate them. You can make two complete sentences by inserting a period. This is the strongest level of separation. You can use a semicolon between the two clauses if they are of equal importance; this allows your reader to consider the points together. You can use a semicolon with a transition word to indicate a specific relation between the two clauses; however, you should use this sparingly. You can use a coordinating conjunction following the comma, and this also will indicate a relationship. Or, you can add a word to one clause to make it dependent.
For example:
- Correct: Every day, millions of children go to daycare with millions of other kids. There is no guarantee that none of them are harboring infectious conditions.
- Correct: Many daycares have strict rules about sick children needing to stay away until they are no longer infectious; enforcing those rules can be very difficult.
- Correct: Many daycares have strict rules about sick children needing to stay away until they are no longer infectious, but enforcing those rules can be very difficult.
- Correct: Daycare providers often undergo extreme pressure to accept a sick child "just this once" because the parent has no other care options and cannot miss work.
Run-On Errors
While a run-on sentence, also known as a fused sentence, might just seem like a type of sentence that goes on and on without a clear point, the technical grammatical definition of a run-on sentence is one that fuses, or "runs together," two or more independent clauses without using punctuation to separate them. The independent clauses may not have any punctuation separating them, or they may have a coordinating conjunction between them, but without the comma that needs to accompany it to separate the independent clauses. For example:
- Incorrect: Every day, millions of children go to daycare with millions of other kids there is no guarantee that none of them are harboring infectious conditions.
- Incorrect: Many daycare centers have strict rules about sick children needing to stay away until they are no longer infectious but enforcing those rules can be very difficult.
- Incorrect: Daycare providers often undergo extreme pressure to accept a sick child "just this once" the parent has no other care options and cannot miss work.
If you locate a run-on sentence and find where the two independent clauses "collide," you can decide how best to separate the clauses. Fixing run-on sentences is very similar to fixing comma splices. You can make two complete sentences by inserting a period. This is the strongest level of separation. You can use a semicolon between the two clauses if they are of equal importance; this allows your reader to consider the points together. You can use a semicolon with a transition word to indicate a specific relation between the two clauses; however, you should use this sparingly. You can use a coordinating conjunction and a comma, and this also will indicate a relationship. Or, you can add a word to one clause to make it dependent.
For example:
- Correct: Every day, millions of children go to daycare with millions of other kids. There is no guarantee that none of them are harboring infectious conditions.
- Correct: Many daycares have strict rules about sick children needing to stay away until they are no longer infectious; however, enforcing those rules can be very difficult.
- Correct: Many daycares have strict rules about sick children needing to stay away until they are no longer infectious, but enforcing those rules can be very difficult.
- Correct: Daycare providers often undergo extreme pressure to accept a sick child "just this once" because the parent has no other care options and cannot miss work.