By Laura Payne
Children generally begin learning about coordinating conjunctions in the third grade and learn how to use them to write compound sentences in the fourth grade. The word so is one of the coordinating conjunctions, but it can also be used as a subordinate conjunction. These two different uses of so have different requirements for punctuation which can lead to confusion. You can help your children remember which so is which by reviewing the following information with them.
Compound Sentences
Compound sentences are created by joining two simple sentences with a comma and a coordinating conjunction. Here are some examples:
Emma went to the library, but the library wasn’t open.
John’s favorite dessert is cake, and his sister’s favorite dessert is pie.
You can choose pizza for dinner, or you can choose tacos for dinner.
Coordinating Conjunctions
There are seven coordinating conjunctions that are easy to remember with the use of a simple mnemonic device. The device is the word fanboys.
F – for
A – and
N – nor
B – but
O – or
Y – yet
S -- so
So as a Coordinating Conjunction
When so is used as a coordinating conjunction, it generally expresses a cause and effect relationship. Here are some examples of so used as a coordinating conjunction (remember that so is always preceded by a comma for this usage):
Joe threw a ball through the window, so his dad replaced it.
Lily had the last sandwich, so Paul had a hot dog.
Ethan’s bike had a flat tire, so he walked to school.
So as a Subordinate Conjunction
Subordinate conjunctions introduce subordinate clauses and are not preceded by a comma. When so is used as a subordinate conjunction, it is actually an abbreviated version of the subordinate conjunction so that. The clause that follows a so subordinate conjunction, usually answers the question why. Because that is optional in this usage, children sometimes mistakenly add a comma before the so.
Here are some examples of properly punctuated sentences with so used as a subordinate conjunction (remember that so is never preceded by a comma for this usage):
Noah threw the ball to Emily so she could catch it.
Grace swims a lot in the summer so she can cool off.
Dad cooked us dinner so mom could go to her book club meeting.
Notice that with each of these example sentences that can be added after the so and the sentence will still have the same meaning and be grammatically correct.
So, Which So is Which?
The best way to practice so usage is to come up with several different so sentences and ask if that can be added after so? If it can, the so is used as a subordinate conjunction and requires no preceding comma. If it can’t, the so is used as a coordinating conjunction and requires a preceding comma.
Here are some unpunctuated sentences to get you started:
1. Mom rang the dinner bell so we would know it was time to go home.
2. Mom rang the dinner bell so we went home to eat.
3. Jake took the skateboard so Abby rode the scooter.
4. Abby rode the scooter so Jake could take the skateboard.
5. The dog chased the cat so the cat climbed a tree.
6. The cat climbed a tree so it could get away from the dog.
Answers: Sentences 2, 3 and 5 require commas because so is used as a coordinating conjunction.
About Laura Payne
A self-confessed language nerd, Laura Payne is the mother of two boys, and she is a part-time English teacher. She has also done freelance writing about several topics including the structure and grammar of English.
