Commas: They're Not Just For English Majors Anymore. commas with...
 
2IC: Two Independent Clauses
(plus a coordinating conjunction)
   
The third comma situation we'll discuss involves joining two independent clauses by using a comma PLUS something called a coordinating conjunction. You might know these types of sentences as "compound sentences."

The basic trick here is to find your commas. If you have one and you've used a coordinating conjuction, there must also be an independent clause on both sides for the comma to be "justified."

But what in the world are "coordinating conjunctions"? Fortunately, there are only seven. Here's an easy way to remember them:
 

F ... For
A ... And
N ... Nor
B ... But
O ... Or
Y ... Yet
S ... So
Hint : if you use a comma to join two independent clauses, then these and ONLY these conjunctions - or "FANBOYS" - can be used with it.
Here's an example:
Beatrice's hair started smoking in the middle of dinner, and it later burst into flames.
Is the comma justified?  The answer can be found by answering two questions:
1) First, check for one of the FANBOYS. Do we have one? Yes: and.

2) The second step, then, is to ask whether what comes on both sides of "and" can stand alone:

  • "Beatrice's hair started smoking in the middle of dinner" can stand by itself because it's a complete sentence.
  • So, too, can "It later burst into flames."
Since both sides are independent, the comma is correct.

Now follow the same procedure for another example:

He had turned into a giant cockroach, yet looked exactly the same.
Does this comma belong here?  The sentence contains a coordinating conjunction, a FANBOY, yet. What comes before yet can stand by itself: "He had turned into a giant cockroach." However, what follows the FANBOY, "looked exactly the same," cannot.
 
Therefore, we cannot justify this comma and must take it out.
CORRECT: He had turned into a giant cockroach yet looked exactly the same.
 
Important:

Notice three common words that are NOT on the list of coordinating conjunctions:
  • however
  • therefore
  • thus

These words are just a few examples of conjunctive adverbs. Very often, writers get into trouble by joining independent clauses with these words.  But remember, they are not FANBOYS.

That means they SHOULD NOT be used along with a comma to join independent clauses--if they are, they will form a comma splice.

Q. Yeah, but what's a comma splice?
A. A comma splice occurs when a comma--and just a comma--is used to join two complete sentences.

Q. How can I tell if I have a comma splice?
A.  Let's have a look on how to look for a comma splice with this sentence:
    This story is exciting, however, I've never read it.
Reading the sentence aloud, it sounds as if the commas might be correct, but let's look closer:
  • First, look at the first comma--the one after "exciting." 
  • Second, ask yourself, "Could what appears on either side of that comma stand alone?"
In this case, yes, both sides can stand alone:
  • This story is exciting.
  • However, I've never read it.

Uh oh. Anytime you join two parts that could have stood by themselves, you create a comma splice. In other words...
 

 This is a

COMMA SPLICE!
 

Q. How can I fix a comma splice?
A. There are several ways, but in this case we might choose one of the FANBOYS to replace "however."  Which one?  "But" works fine.  So does "yet."

  • The story is exciting, but I've never read it.
  • The story is exciting, yet I've never read it.
Don't forget that the comma splice could also be corrected by leaving "however" in and replacing the first comma with a semi-colon or a period.
  • The story is exciting; however, I've never read it.
  • The story is exciting. However, I've never read it.

Before moving on, and since it's all so exciting, we should also mention subordinating conjunctions. Subordinating conjunctions are words that signal a subordinate or dependent clause. Examples include
  • while
  • because
  • since
  • before
  • after
Like the coordinating conjunctions, the FANBOYS, these words can join clauses. But remember, they are not FANBOYS, so they usually SHOULD NOT be used with a comma.
INCORRECT: We had hamsters for dinner, because we were out of hamburgers.

CORRECT: We had hamsters for dinner because we were out of hamburgers.
Because is a subordinating conjuction.  We have clauses that can stand alone on both sides of "because," but since "because" is not one of the FANBOYS, we don't need a comma.

Just for review, see if you know what happens if we place the second part of this sentence at the beginning.

Now we have the subordinate clause, which you might recognize as an introductory element, in front of the independent clause. So a comma belongs after "hamburgers."
 
next (CA)

Intro, Get Started, IE, CE, 2IC, FANBOYS, CA, NRE, Review
 
IE: Introductory Elements
CE: Contrasting Elements
2IC: Two Independent Clauses
CA: Compound or Coordinate Adjectives
NRE: Non-Restrictive Elements
A Few Other Situations (quotations, lists, etc.)