Today I’m going to get nitty-gritty with some English grammar. A few years back I did a series of these types of posts that I called Punctuation 101. This led to my little book Punctuation 101. So, if you’re curious, check out some of those posts. I’ll also link to them by subject at the end of this post.

Before I get started, I want to just vent a little. Why, creators of the English language, do we have to have so many weird words for grammar? Why do we need to have multiple names for the same thing? Teaching this to myself was hard enough, but teaching this to fifth graders is a big challenge.

Thanks for letting me get that off my chest. I’m going to use the correct terms in this post, and put the other, often more easy to understand terms in parentheses beside it. Hopefully that will help keep any confusion at bay.

So, can you tell the difference between a simple sentence, a compound sentence, and a complex sentence? Do you know when to use a comma? When to leave it out? Let’s take a closer look.

Simple Sentences

A simple sentence is an independent clause that expresses a complete thought. It has a single subject (noun) and a single predicate (verb). This subject and predicate are actually a team, since the subject needs to be doing the action in order to create an independent clause.

Luke ate the hamburger.

Beyond that very simple sentence I just shared, there are two other types of simple sentences, but before I tell you what they are, I want to talk about this word: compound.

Whenever you see the word “compound” in grammar, it’s going to be “pounding” two more more things together.

Let’s go back to our two, slightly less-than-simple sentence types. The first is a sentence that has a compound subject (noun). All that means is that there are two or more subjects (nouns) teaming up with the predicate (verb), both completing that same action.

Jack and Jill went up the hill.

Two people, doing the same action. It’s still a simple sentence, but it has a compound subject (also called a compound noun).

The other slightly less-than-simple sentence type has a compound predicate (verb). You guessed it. That means there is one subject (noun) teaming up to complete more than one action.

The dog ran and barked.

One subject (noun) doing two actions (verbs) creates a compound predicate (also called a compound verb).

No commas needed. Yet.

Compound Sentences

A compound sentence has two or more independent clauses that are hooked together with a comma and a coordinating conjunction, like the word “and.”

Luke ate the hamburger, and he was full.

Why the comma? You need a comma with that coordinating conjunction because without it, you’ll have a run-on sentence. I’ve always thought of it like this: a coordinating conjunction is too little to hold together two complete sentences on its own. It needs the added help of a comma. (Imagine that comma’s hook just latching on and holding on for dear life!)

Luke ate the hamburger and was full.

Since “was full” is not a complete sentence (it doesn’t have a subject!), the coordinating conjunction is strong enough to hold things together. This is actually a simple sentence with a compound predicate (verb). No comma needed.

Another way to look at it is that a coordinating conjunction coordinates. It likes things to match on both sides. If there is a complete sentence on both sides, it needs that comma to help it. But if it is merely attaching two words, then it wants to keep that even too and it doesn’t need a comma to do it.

Coordinating Conjunctions

There are seven coordinating conjunctions. They give equal importance to the words or sentences they connect. You’ve likely heard of the acronym FANBOYS to remember them by. Here is an image I made with examples for each. Note how I highlighted each coordinating conjunction in the example sentences and, if they needed one, the comma that goes with it. Look and see if you can identify independent clauses (and their subject-verb teams) on either side of the sentences that contain commas.

Complex Sentences

A complex sentence has an independent clause and a dependent clause (also called a subordinate clause). A dependent clause is a group of words that has a subject and a verb but does not express a complete thought. Because of this, it is not a complete sentence and cannot stand on its own.

Luke was full when he ate the hamburger.

Above, “Luke was full” is an independent clause. It has a subject-verb team and expresses a complete thought. However, “when he ate the hamburger” does not express a complete thought. It does have a subject-verb team with “he” and “ate” but that pesky word “when” (which is called a subordinating conjunction) messed up a perfectly good sentence. It broke things.

I looked up the definition of the word subordinate. It means a person under the authority or control of another. I picture an angry coach yelling at a player on his team or a drill sergeant yelling at a private. That player and that private are subordinate to the coach and the drill sergeant.

Subordinating Conjunctions

A subordinating conjunction is a word or phrase that links a dependent clause to an independent clause. There are MANY subordinating conjunctions. Here are a bunch.

Subordinate and dependent mean the same thing in grammar. While we imagined that player and private being subordinate to the coach and the drill sergeant, we can also picture a mother and a baby or a nurse and an injured patient. The baby and the patient are dependent upon the mother and the nurse. So it is with dependent (subordinate) clauses. These groups of words are not in the right order to stand on their own. They need the help of more words to make them complete.

I ran outside. (independent clause)

(But if I add a subordinating conjunction to the beginning . . .) As soon as I ran outside.

The subordinating conjunction breaks my sentence. Now its a sentence fragment, and I need to fix it.

As soon as I ran outside, I slipped on the ice. (I added an independent clause.)

Note: Whenever a complex sentence begins with a dependent clause, a comma must separate the two clauses.

As soon as I ran outside, I slipped on the ice.

I slipped on the ice when I ran outside.

When Luke ate the hamburger, he was full.

Luke was full when he ate the hamburger.

So, there you have it. A little grammar review and a few comma rules to help you to stronger first draft writing—or at least a better understand when you go back to edit.

Need more help with the nitty-gritty? Here is a list of my Punctuation 101 blog posts:

Punctuation 101: Dialogue Tags
Punctuation 101: The Comma
Punctuation 101: The Colon
Punctuation 101: The Semicolon
Punctuation 101: Dashes and Ellipses
Punctuation 101: Apostrophes
Punctuation 101: Quotation Marks
Punctuation 101: Numbers

Any questions? Do you struggle with too many or too few commas? Do you struggle with runon sentences, comma splices (when you use the comma but forget the conjunction), or sentence fragments (that you didn’t do on purpose, because I LOVE sentence fragments in fiction)? Share in the comments.

Jill Williamson is a chocolate loving, daydreaming, creator of kingdoms, and the author of several young adult fantasy novels including the Blood of Kings trilogy. She loves teaching about writing. She blogs at goteenwriters.com and also posts writing videos on her YouTube channel and on Instagram. Jill is a Whovian, a Photoshop addict, and a recovering fashion design assistant. She grew up in Alaska without running water or electricity and now lives in the Pacific Northwest with her husband and two kids. Find Jill online at jillwilliamson.com or on InstagramYouTubeFacebookPinterest, and Twitter.