A compound sentence is made up of two independent clauses joined together with a coordinating conjunction.
There are several coordination conjunctions. You know the list: and, but, or, nor, so, for, yet, and so. Another way to remember them is the use of the acronym, FANBOYS.
An independent clause is a sentence that can stand on its own. At the very least, it has a subject at verb.
Jack was a great kisser.
Steve really knew how to dance.
Let’s combine those to make a compound sentence.
Jack was a great kisser, but Steve really knew how to dance.
Jack was a great kisser, and Steve really knew how to dance.
Notice the comma placed before the coordinating conjunctions? Most of the time you will want to include those, but you may have been told by English teachers over the years that they are unnecessary. These teachers may have come from a journalism background where commas are often omitted to save paper and ink. In the world of fiction, however, commas are our friends. They allow us to influence reading speed, which impacts how readers interpret the tension in the story. But commas are also there to help readers make greater sense out of our words. There are times where you won’t need the comma in a compound sentence, but overall, it helps with readability.
When would you want to exclude the comma? When the sentences are highly related.
Jack was a great kisser and he really knew how to use his tongue.
The second independent clause describing his amazing tongue is so closely related to the kissing that I wouldn’t put a comma in here. Is it wrong to put one in? No. You certainly can, especially if you want to slow the pacing, but pay attention to the sentences around the one you’re working on. Variety is the spice of life, and many readers take a mental breath when they see a comma. If nearby sentences are filled with commas, leave out the optional ones. No need to make your readers hyperventilate. 🙂
That brings me to another exception to the commas-in-compound-sentences rule. If you are at the climax of your story and you want your reader to pick up the pace of their reading, then leave the comma out. I just did in that last sentence. See? I wanted you to read it quickly, so I left off the comma before and. I would reserve this for moments where you really want the reader to feel as if they can’t catch a breath.
If you have any more questions about compound sentences and commas, please feel free to leave them below. Eventually, I’ll get to more complex compound sentences with introductory phrases squished in between.