English 104: College Composition

Learn more about comma usage from the pros! There are just too many ways to use the comma (it's a basic punctuation mark, after all) to fit in one sentence. Watch here to learn about some of the more common traps students fall into when trying to put commas in the right place.

Avoid Confusion

Knowing where to put commas in a sentence can be tricky, especially because seemingly similar-looking sentences require different comma usages. Oftentimes, it helps to verbalize the sentence out loud if you're not sure where the commas are supposed to go, listening to where you would naturally pause. In some instances, however, even that won't work.

Use Commas To Separate Independent Clauses

Normally, when there are only two pieces of a sentence connected by a conjunction like 'and,' you wouldn't need a comma in between them - as in, 'I like swimming through fire and juggling bobcats.' However, any time you have two independent clauses in the same sentence - an independent clausebeing a clause with at least one subject and one verb that can stand on its own as a sentence - they need more than just a comma to separate them. Instead, they have to be separated by either a semicolon, a colon, or a comma accompanied by a coordinating conjunction - as in, 'I like swimming through fire, but I love juggling bobcats.'

If you wrote:

I like swimming through fire, I love juggling bobcats.

you would be committing a grammatical error called a comma splice. However, add any comma plus a coordinating conjunction - you can use the mnemonic FANBOYS (for, and, nor, but, or, yet, and so) to remember which conjunctions are considered coordinating conjunctions - and you're all set.

I ran to stop him, for he was letting the dragon level Tokyo.

Use Commas To Separate Non-Essential Elements

Sentences are made up of essential and non-essential clauses (another name for the main clause is the essential clause). When you've got a non-essential clause in a sentence, it needs to be offset with commas. Here's an example:

Jonathan, though he was destined to become King of the Spider-People, just wanted to be an accountant.

The middle part there, 'though he was destined to become King of the Spider-People,' can easily be pulled out of the sentence and the sentence will still make sense - that is, it would read, 'Jonathan just wanted to be an accountant.' Therefore that middle clause is non-essential, and it needs to have commas offsetting it on either side. A non-essential clause also can't stand on its own as a sentence, which is one way to help you decide whether it needs those commas or not.

You can also offset non-essential clauses with dashes, as in, 'Jonathan - though he was destined to become King of the Spider-People - just wanted to be an accountant.' It's the same rule, and it sounds pretty similar when I read it, except that the dashes pop the non-essential element out more for the reader and are therefore more appropriate when you want to highlight that a certain element or characteristic is particularly special.

Use Commas To Separate Contrasting Parts

You should also place a comma when two parts of the sentence contrast each other. This is a case where you don't need a conjunction or a semicolon to separate the clauses. For instance:

He was laughing at you, not with you.

The samurai was reserved, almost stoic.

Another special case like this is when you want to indicate a natural pause (this is the primary use of the comma and how it sounds in our speech, after all) - as in: 'You've been paying close attention to this lesson, haven't you?' You will need a comma when you ask a question at the end of a sentence in this manner.

Use Commas To Eliminate Confusion

We touched on this a little bit in the previous comma lesson when we talked about the Oxford comma - that's the one that appears last before the conjunction when you're writing a list of things - and the general rule is the same as the specific was in that case. If putting a comma in makes the sentence clearer, then put it in. If it doesn't, leave it out. Let's look at one key example and how commas affect it.

When prepping for space flight practice is essential.

Right now, we've got a run-on sentence. There needs to be some punctuation in here, but where we put the comma completely changes the meaning of the sentence. If we put it here:

When prepping for space, flight practice is essential.

the meaning is different than if we put it here:

When prepping for space flight, practice is essential.

The first sentence suggests that flight practice is an essential part of getting ready to go to space. The second sentence suggests something a little more nebulous - we don't actually know what kind of practice you need to go to space. It could be 'space flight practice,' but it might not be. Where you put the comma decidedly changes how clear the meaning of the sentence is.

Lesson Summary

When it comes to comma usage, practice makes perfect, but keep in mind a few rules (and refer back here if you need to for a refresher) and you'll be in good shape. Remember that:

1. You can use a comma and conjunction to separate two independent clauses - as in, 'Globulon loves conquering tiny planets, but his partner, Terry, prefers gardening.'
2. You can always use commas to offset the non-essential parts of a sentence - as in, 'Silencio and Cubo, the famous mime duo, were set to perform on stage that night.'
3. You can use commas to offset contrasting parts of a sentence, such as, 'The Yeti isn't evil, just misunderstood.'
4. You should also include the comma when it clears up confusion, and omit a comma when it makes the sentence less clear.