Student: So, I think I have the coordinating conjunctions figured out. They are and, but, or, for, nor, so, and yet. But I still don’t understand how to know if I need a comma when I use one or not.
Professor: This can definitely be confusing, but I can help clear up the confusion! Just because you have an “and,” or any other coordinating conjunction, in your sentence doesn’t mean you need a comma. You have to think about what’s around that “and.”
Student: This still seems confusing. Can you give me an example?
Professor: If you are using a word like “and” or “but” to separate two independent clauses, you should add a comma.
Here is an example:
I should not have stayed up so late watching scary movies, but I could not tear myself away from another good ghost story.
In this instance, the “but” is separating two independent clauses, so you have to place a comma with the coordinating conjunction to make a proper “boundary” between those two sentences. In this case, the “comma” with the word “but” work together a lot like a period does to separate these two complete thoughts.
Student: That makes sense. So, a comma with a coordinating conjunction makes a kind of sentence boundary. Only, it does not make the stop like a period does.
Professor: Right! And, if you change the sentence so that you are not separating two independent clauses with the coordinating conjunction, you should not use a period. Here is the example:
I should not have stayed up so late watching scary movies but could not tear myself away from another good ghost story.
Now, the “but” is no longer separating two independent clauses, so you should not place a comma here. The “but” is simply joining two phrases to make a compound predicate.
Student: I think I get it. It really depends on what the coordinating conjunction is connecting. If I am trying to connect independent clauses, I need a comma with my coordinating conjunction. If I am not, I don’t need the comma.
Professor: Exactly! Remember, you have to stop and think about how you are trying to use commas before you can know for sure if you need to use one.
This presentation was brought to you by the Excelsior Online Writing Lab.