Commas with Compound Sentences
By Tina Blue
March 14, 2002
A compound sentence consists of two or more independent (main) clauses. Because the independent clauses in a compound sentence are grammatically equal structures, they are joined by one of the coordinating conjunctions (and, but, yet, or, nor, so) or by a set of correlatives (either-or, neither-nor, not only-but also, both-and).
In general, when the independent clauses in a compound sentence are joined by a coordinating conjunction, they are separated by a comma.
The comma precedes the coordinating conjunction. A common error is to place the comma after the conjunction:
WRONG: We picked them up early but, they still missed their plane.
RIGHT: We picked them up early, but they still missed their plane.
WRONG: I hadn't seen my nieces and nephews for ages so, I went overboard on buying them Christmas gifts.
RIGHT: I hadn't seen my nieces and nephews for ages, so I went overboard on buying them Christmas gifts.
WRONG: Do you want to stay behind or, will you come with us?
RIGHT: Do you want to stay behind, or will you come with us?
Most of the time (treat it as about a 90-95% rule) you should use a comma between the independent clauses in a compound sentence. But occasionally it is permissible, and sometimes even preferable, to leave that comma out.
The current trend in American style is toward minimal punctuation. In other words, commas are seen as speedbumps, and we don't want unnecessary obstacles to slow down our readers. Many permissible commas can be left out of sentences where they once might have been required, or at least strongly preferred.
Under certain circumstances, the comma between independent clauses in a compound sentence can be left out, and sometimes even should be left out.
Here are the guidelines for deciding whether to omit the comma in a compound sentence.
1. If both independent clauses are quite short, especially if the two clauses are very closely related, and even more so if the subject of both clauses is the same.
~ He threw me the book and I dashed out the door.
~Linda washed the dishes and Naomi cleaned up the living room.
~I've been waiting for this letter but now I wish it hadn't come.
2. Even if only the first clause is quite short, especially if the two clauses are very closely related, and even more so if the subject of both clauses is the same.
~ Debby left home early but she wasn't able to make it to her class on time because the buses were running late.
~You have to write that paper tonight or you will almost certainly lose points for turning it in late.
(In each of these cases, you can use the comma if you prefer, but you also have the option of omitting it.)
NOTE: Never omit the comma if there is any chance that your sentence will be misread, even if only for a moment.
AMBIGUOUS: We finished eating dinner and then the children cleared the table.
IMPROVED: We finished eating dinner, and then the children cleared the table.