A problem many native English writers and foreign English learners have in common is combining independent clauses without the appropriate punctuation or conjunctions, often seen with what we call comma splices.

I thought this would be an interesting topic to cover, especially as I realised it’s not already in my Advanced Writing Skills book (and it’s a nice follow up to my recent look at serial commas!). So, I’m going to briefly explain what comma splices are, why (and how) they should be avoided and why they can sometimes be acceptable.

What is a Comma Splice?

Simply put, a comma splice is when you have a comma combining independent clauses, where you would otherwise expect to see a conjunction or conjunctive punctuation (for example a semi-colon, colon or dash), or two separate sentences. For example:

She went into the basement. The lights weren’t working. = separate sentences
She went into the basement but the lights weren’t working. = conjunction
She went into the basement; the lights weren’t working. = conjunctive punctuation
She went into the basement, the lights weren’t working. = comma splice

To break this down a little more, and help identify such splices, remember that an independent clause occurs whenever we have a new verb and subject, without any connectors that link it dependently to another clause (e.g. subordinating conjunctions like when, as, or relative pronouns like who, which).

In the example above, the verbs “went” and “weren’t” indicate distinct clauses, made clearer because we have separate subjects “she” and “the lights”. However, even if the verbs share a subject, which does not necessarily need to be repeated, a new active verb can still form a separate independent clause that needs connecting:

She went into the basement and tried to turn on the light. = conjunction
She went into the basement – tried to turn on the lights. = conjunctive punctuation
She went into the basement, tried to turn on the lights. = comma splice

The second example here, with the dash, creates a sentence fragment, which can be more acceptably linked by a dash than a comma (though depending on the context even the dash might not be welcome; as always, the more formal a text, the more likely it would be to stick to expected rules and conventions).

Why do Comma Splices Matter?

In the examples above, the comma splices are technically incorrect. You might read them and think they make sense, though, so why does it matter? When compared to sentences that use semi-colons to bridge clauses, it might look like there’s little difference, after all.

Well, the simplest explanation is that commas are not intended to be used in this way and it’s therefore likely to cause confusion with readers. It can actively affect the way a sentence is read. How problematic this is depends on the sentence; the examples above aren’t confusing, but longer sentences or ones with different subjects could be. It can also make it more difficult to read as we won’t pause in the right places, creating a clumsy flow where information isn’t clearly separated:

She went into the basement, the lights weren’t working, it was very dark.

By using a comma, we’d also miss the opportunity to demonstrate how separate ideas are connected. Without more context, for example, we could easily express different scenarios depending on the chosen connector:

She went into the basement where the lights weren’t working.
She went into the basement because the lights weren’t working.

But if you read enough in English, particularly in fiction, you’re almost guaranteed to come across some comma splices eventually. It’s an easy mistake to make, and an easy one to miss. It’s also sometimes done deliberately. This is most often the case where a writer wants to add information running directly on without distinct connectors. It’s less formal than using a semi-colon and more subtle than using a dash, both of which would be the more accepted styles. It can create a slightly different feel when we have a shared subject with a follow-on action that adds a response or feeling. Compare:

She muttered under her breath; hated the dark.
She muttered under her breath – hated the dark.
She muttered under her breath, hated the dark.

In this example, it’s actually working similarly to an adverbial, but it gives it a particular twist: “hating the dark” would be the expected, grammatically correct form, but “hated the dark” sets the verb differently, as a rule, or a complete, emphatic action.

That said, it’s a technique that few writers can get away with. I read an Elmore Leonard book (Maximum Bob I believe) which was full of comma splices, for example, but Elmore Leonard was an exceptional writer with a very specific style (in this case often reflecting a character of a certain low class’s mode of language). It’s very much a case of only bending the rules when you have mastered them, and even then only if you can confidently justify why you’re doing it – and note that it is only justifiable in very specific circumstances, which will often fall into the realm of deliberate mistakes anyway.

How to Avoid Comma Splices

Once you’ve got the hang of identifying independent clauses, to avoid comma splices ask yourself if your clauses are appropriately connected. If you find they’re not, this is fairly simple to fix. Let’s go back to our original example:

She went into the basement, the lights weren’t working.

Most simply, we could separate the clauses into separate sentences:

She went into the basement. The lights weren’t working.

To demonstrate a particular relationship between clauses, or generate a particular flow, you could replace the comma with an appropriate conjunction:

She went into the basement but the lights weren’t working.

To connect the clauses closely, speeding the text up and demonstrating a relationship without spelling it out, you could use a semi-colon:

She went into the basement; the lights weren’t working.

This could also be done with a dash, though the choice here is a matter of style and (as with the splices themselves) dashes might not be universally accepted. Also note that conjunctive punctuation like this might bridge the clauses correctly, but it doesn’t necessarily make much sense as a choice if there isn’t a clear reason that they’re closely connected. In this example, for example, it would work better if we had an indicator of why the clauses are connected, such as an adverb:

She went into the basement slowly; the lights weren’t working. (the second clause accounts for how she went, slowly)

I hope this helps as a bit of a crash course in comma splices; there’s certainly more nuance that we could go into them and the examples you find in the wild can lead to lots of questions. There’s also controversy connected to this. Purists will say comma splices are unacceptable at any time (and if you want to be safe that’s a reasonable view to follow), whilst others may use them consistently, and clearly, without even knowing how or why. It’s one of those areas of English that can cause arguments, but as with all these things, the trick is to understand how and why it happens, and from there you can decide for yourself how and why it matters.