The comma separates the structural elements of a sentence into manageable segments.
Rules for Comma Usage
- Use a comma to separate three or more words, phrases, or clauses written in a series. (A comma is necessary before the last ‘and.’)
The Constitution establishes the legislative, executive, and judicial branches of government.
- Use a comma after transition words and phrases that begin a sentence: however, therefore, on the other hand, for example, etc.
Today is a national holiday. Consequently, most stores are closed. (word)
Today is a national holiday. As a result, most stores are closed. (phrase)
- Use a pair of commas in the middle of a sentence to set off transition words and phrases as well as clauses that are not essential to the meaning of the sentence.
I appreciate your hard work. In this case, however, you seem to have over-exerted yourself. (word)
This restaurant has an exciting atmosphere. The food, on the other hand, is rather bland. (phrase)
Next Tuesday, which happens to be my birthday, is the only day I can meet. (clause)
- Use a comma to separate independent clauses when they are joined by any of these seven coordinating conjunctions: for, and, nor, but, or, yet, so [FAN BOYS].
The game was over, but the crowd refused to leave.
- Use a comma after a dependent clause when it comes before the independent clause.
While I was eating, the cat scratched at the door.
Because I was late, I had to sit in the back.
NOTE: Do not use a comma if the order is reversed (the independent clause comes before the dependent clause), except for cases of extreme contrast. A dependent clause provides additional information about the independent clause and establishes the relationship of this information to the independent clause. The most common subordinating conjunctions are: after, although, as, as if, because, before, even though, if, since, so that, than, that, though, unless, until, when, where, whether, and while.
She was late for class because her alarm clock was broken.
She was still quite upset, although she had won the Oscar. (extreme contrast)
- Use a comma to set off all geographical names, items in dates (except the month and day), addresses (except the street number and name), and titles in names.
Birmingham, Alabama, gets its name from Birmingham, England.
Rachel B. Lake, MD, will be the principal speaker.
- Use a comma to shift between the main discourse and a quotation.
John said without emotion, “I’ll see you tomorrow.”
- Use a comma wherever necessary to prevent possible confusion or misreading.
To George, Harrison had been a sort of idol.