We’ve all heard that you place a comma where the reader takes a breath. That, however, is just a starting point, Elizabeth, and some sentences, like this one, might cause hyperventilation.
More than breath marks, commas corral ideas, making them clear to readers the first time they read.
What are the basic comma rules?
The following comma rules make for clear, correct writing.
Rule 1: Use a comma and a conjunction to form a compound sentence.
You can join two related simple sentences using a comma and a coordinating conjunction (and, but, or, nor, for, so, yet).
I wrote to Jerry. Marlo spoke to Shanise.
I wrote to Jerry, and Marlo spoke to Shanise.
The comma shows where the first idea ends and the next begins. It helps readers find the subject-verb pattern that unlocks meaning. Look what happens without the comma:
I wrote to Jerry and Marlo spoke to Shanise.
At first, you think that “I wrote to Jerry and Marlo,” but then you hit the verb “spoke” and realize “Marlo” is the subject of a new thought. You have to reread the sentence to make sense of it, or maybe you just give up altogether–all for lack of a comma.
Note: In a compound sentence, you need both the comma and the conjunction. If you leave out the conjunction, you have an error called a comma splice. If you leave out both, you have an error called a run-on sentence.
Rule 2: Use a comma after introductory words.
Place a comma after an introductory phrase of four or more words or after any introductory clause.
While I wrote to Jerry, Marlo spoke to Shanise.
The reason is the same–helping the reader find the subject-verb pattern of the main clause. Here’s the sentence without the comma:
While I wrote to Jerry Marlo spoke to Shanise.
You first think his name is “Jerry Marlo” until you hit that verb “spoke” and have to reread the sentence just to make sense of it. One little comma makes the ideas clear the first time through.
Rule 3: Use commas to separate items in a series.
A series is a list of three or more items.
I admire my parents, Lady Gaga, and Tony Bennett.
The comma before the “and” is called the series comma or Oxford comma. Associated Press style does not use it, but most other style guides do, and leaving it out can cause confusion.
I admire my parents, Lady Gaga and Tony Bennett.
Without the series comma, it seems that Lady Gaga and Tony Bennett are my parents. That’s confusing (though it might be lucrative). Here’s another example.
The sandwich options are ham and cheese, peanut butter and jelly, and bacon and tomato.
Leaving out the comma creates confusion.
The sandwich options are ham and cheese, peanut butter and jelly and bacon and tomato.
Is it a peanut butter and jelly and bacon sandwich? Or a jelly and bacon and tomato sandwich? Once again, the lowly comma makes meaning clear.
Rule 4: Use commas to separate equal adjectives.
When two adjectives equally modify the same noun, place a comma between them.
I proposed a bold, beautiful plan.
You know that two adjectives are equal if you can switch their order or if you can put and between them.
I proposed a beautiful, bold plan.
I proposed a bold and beautiful plan.
If adjectives do not equally modify the same noun, don’t use a comma.
I bought a red sports car.
I bought a sports red car.
I bought a red and sports car.
Rule 5: Use commas to set off extra information.
If a phrase or clause could be dropped from a sentence without changing its meaning, place commas around it.
My father, who is an engineer, likes classical music.
You could drop “who is an engineer” from the sentence and it would still make sense: My father likes classical music. The commas that set off this extra information once again help readers find the subject-verb pattern.
When a phrase or clause cannot be dropped without changing the meaning, do not set it off with commas.
Classical musicians who practice daily perform better than those who practice weekly.
If we dropped these “who” clauses, we’d have a nonsensical sentence.
Classical musicians perform better than those.
These clauses are essential, so they should not be dropped and should not be set off with commas.
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