“Commas!” That’s the invariable response when I ask a writing group what they’d like to work on. “Where do they go?” “How do I know when to use a comma and when to use a period?” “Is there a way to tell if I’m using too many commas–or not enough of them?”

The good news is that by learning just three comma rules, you’ll be able to punctuate just about everything. The even better news is that once you’ve learned these three rules, you’ll also know how to use semicolons, avoid sentence fragments, and spot run-on sentences.

It all boils down to one basic principle: Learning the difference between a sentence and an extra idea. Master this skill, and the rest is easy. That’s a promise! (Hint: Using a colored highlighter to mark up your rough drafts is a huge timesaver when you’re placing commas–I’ll show you how.)

Let’s get started!

1. Everything that is said or written falls into one of two categories: A sentence or an extra idea. (Everything! You can count on it.)

Sentences:  Iwent to the mall. Jerry called me last night. Weekends are always too short for the things I want to do. Maine gets very cold in the winter. The sky was full of stars.

Extra ideas:  Because I mailed the payment late. When the alarm went off. In two minutes. Unless you prefer the plain breadsticks. Although I wasn’t speeding.

2. Sentences end with periods. Extra ideas end with commas.

How Do Sentences and Extra Ideas Work?

Sentences can stand by themselves. Extra ideas can’t. They have to be glued on to a sentence.

Take a look at these examples:

Because I mailed the payment late, I was charged a late fee.

When the alarm went off, Dan leaped out of bed.

In two minutes, I’ll be back with a refill for your coffee.

Unless you prefer the plain breadsticks, I’ll order them with garlic.

Although I wasn’t speeding, the police officer pulled me over.

Guess what? You’ve just learned about 70% of what you need to know about punctuation! (To learn more, click here.)