Comma Splices

Grammatical Explanation

So what are independent clauses, and how do you properly join them?

Independent clauses are strings that have a subject and a verb and can stand on their own -- like Blue is really trendy this year and She drove to work. You could put a period at the end of either of those strings, and it would be fine. Notice that we could add some words that would make it impossible for those strings to stand on their own -- like Because blue is really trendy this year” or And then she drove to work. These would both be incomplete sentences -- or “fragments” -- which means they’d need another independent clause to attach themselves to.

So you could say, for example: Because blue is really trendy this year, we should paint our bedroom or Emily called the pharmacy, and then she drove to work. That would be great. Generally speaking, building bigger sentences like this from small ones, a process some people call "sentence combining," helps you articulate richer, more complicated thoughts.

But here's the issue: you can’t just run “independent clauses” together with a comma, like “Blue is really trendy this year, we should paint our bedroom” or “Emily called the pharmacy, then she drove to work.” That’s a comma splice.

Fixing a Comma Splice

To eliminate a comma splice, you can do one of four things:

1. Add a comma and a coordinating conjunction, like:

He saw Joel and Alexa there, and they all had a lot of fun.

2. Replace the comma with a semi-colon, like:

He saw Joel and Alexa there; they all had a lot of fun.

3. Separate into two sentences, like:

He saw Joel and Alexa there. They all had a lot of fun.

4. "Subordinate" one of the two sentences, working it into the other by restructuring the sentence, like:

Because he saw Joel and Alexa there, they all had a lot of fun.

Or: Seeing Joel and Alexa there, he knew they'd all have a lot of fun.

Fine Point: A Note on Semi-Colons

Lots of writers like to use semi-colons because, well, they just look really smart! To many readers, they seem formal and thoughtful, especially in academic writing.

But many writers also use them in the wrong situations (which of course doesn't look smart at all!).

In all but a few very limited contexts (like legal contracts or scientific documents, for example), semi-colons are used only in the way we've demonstrated above. There needs to be an independent clause -- that is, a subject and verb that can stand on their own -- on each side of the semi-colon. They're used in order to suggest that there's a close conceptual relationship between two sentences. Instead of separating them with periods, you combine them with a semi-colon. Like:

April is often rainy; July is always dry.

It's very hard to predict when it will snow in Oswego; you have to know exactly what direction the wind will blow and just how hard.

He made the call; moments later, a car pulled into the driveway.

In specific sorts of documents where there are often long lists of items likely to have internal commas, semi-colons are also used instead of commas to separate those listed items. Again, legal contracts and scientific documents are good examples.

Fine Point: A Note on However and Therefore

People often use words that offer cues to readers about the connections between sentences. Grammarians call these words "conjunctive adverbs" or sometimes "sentence adverbs."

Two that often get misused are however and therefore -- which you'll notice mean pretty much the same thing as but and so. But while they mean the same thing about the relations between ideas, they do something different in sentences: that is, they don't have the same grammatical function.

Misusing them creates what's technically a comma splice.

Here's the idea: conjunctive adverbs are small words or phrases you might throw into a sentence almost anywhere to suggest the relationship of one sentence (or independent clause) to a previous one. These are words or phrases like furthermore, for example, in fact, conversely, on the other hand, etc. But sometimes people use them as coordinating conjunctions, which have the power to join independent clauses in compound sentences. When they work like this, coordinating conjunctions must appear in the middle of those two clauses. Like: The door slammed, and he jumped.

So while they can mean the same thing, they can't be used interchangeably in sentences.

That is, you can say I was hungry, so I ate some popcorn. But it would be a comma splice to say: I was hungry, therefore I ate some popcorn. Similarly, you can say: It was good, but it didn't satisfy me for long. But it would be a comma splice to say: It was good, however it didn't satisfy me for long.

So what can you do if you want to use however or therefore?

You can say:

I was hungry; therefore, I ate some popcorn.

It was good; however, it didn't satisfy me for long.

I was hungry. Therefore, I ate some popcorn.

It was good. However, it didn't satisfy me for long.

I was hungry; I ate some popcorn, therefore.

It was good; it didn't satisfy me for long, however.

I was hungry; I therefore ate some popcorn.

It was good; it didn't, however, satisfy me for long.

Again, this is because so and but are coordinating conjunctions -- they combine independent clauses to make compound sentences. But conjunctive adverbs, on the other hand, have no structural power at all; they only modify the relation of the second independent clause to the first.

This isn't an error as serious as the kind of sentence people usually identify as a comma splice: I ate some popcorn, it didn't satisfy me for long. But it does show a level of technical control your instructors -- and other readers in formal contexts -- will appreciate.