The comma splice: how to avoid the most common punctuation error there is
The full-stop - also known as the period - has several uses.
But it’s most often used at the end of a declarative sentence. That’s just a fancy way of saying a sentence that’s making statement. As opposed to asking a question or making an exclamation - where you’d obviously use a question mark or an exclamation mark.
Now, to understand how to use the full stop correctly in a declarative sentence, you have to understand what a sentence is.
So let’s dial back a bit and ask ourselves: what is a sentence?
Here’s the usual dictionary definition:
A sentence is “A set of words that is complete in itself, typically containing a subject and predicate”
Let’s quickly unpack some of that grammar speak here. First of all, ‘subject’ means the person or thing that’s doing the action of the sentence.
And ‘predicate’ means the part of the sentence that contains the verb - or the action word - and states something about the subject.
For example, in the sentence ‘Jamie eats’, Jamie is the subject, while the verb or action word ‘eats’ is the predicate.
But remember: the predicate is defined as the part of the sentence containing the verb. So sometimes the predicate might be longer as in: Jamie eats dinner. Here, the entire phrase ‘eats dinner’ is the predicate.
Or we could even say: Jamie eats dinner after eight o’clock each night. And here, ‘eats dinner after eight o’clock each night’ is the predicate.
Each of these three examples - Jamie eats, Jamie eats dinner, and Jamie eats dinner after eight o’clock each night - is a set of words complete in itself containing a subject and a predicate. So each is a full sentence.
It’s really important to understand this definition of a sentence, because probably the number one error I spot in people’s writing is not ending sentences with a full stop. Instead, they will often join two separate sentences with a comma.
This hugely common error is known as a ‘comma splice’. So let’s take a look at a real-life example of a couple of comma splices that I came across recently.
I’ve changed some of the details to protect the author, but this extract is from a sales letter. It has two full stops in it, but it actually needs four:
I am from TTFN, a firm which specialises in corporate strategy advice, we currently advise many real-estate developers across both the UK and continental Europe.
We also advise the social housing, private equity and infrastructure sectors, I have attached a brochure for your reference.
Let’s start with that second sentence - which is actually two sentences wrongly joined by a comma.
If we take all the text before the second comma, we can see that it meets all the criteria for a sentence.
First of all, it’s a set of words complete in itself: We also advise the social housing, private equity and infrastructure sectors makes total sense on its own.
It also has a subject (We) and a predicate (the part of the sentence that includes the verb - also advise and so on).
Let’s also look at the text after that comma in the middle. Again, it fulfills all the criteria for a sentence: I have attached a brochure for your reference is a set of words complete in itself - it doesn’t need anything else to makes sense. And it has a subject (the I that’s doing the action) and a predicate (the part of the sentence that includes the verb - have attached a brochure for your reference).
So what we have here is two complete sentences. And in correct grammar, you cannot connect two separate sentences with a comma. You may see this habit a lot, but a full-stop would generally be considered the correct choice here.
Let’s look at the first sentence - which again, strictly speaking, is two sentences wrongly separated by a comma.
I am from TTFN meets the criteria of a full sentence. It is a set of words complete in itself and it’s made up of a subject (I) and a predicate (am from TTFN).
So we could put a full stop here instead of the first comma.
If we did that, the next sentence would read:
A firm which specialises in corporate strategy advice,we currently advise many real-estate developers across both the UK and continental Europe.
Again, this satisfies the criteria of a full sentence. We have a subject: A firm which specialises in corporate strategy advice, we. It’s obviously a little more complex than the previous subjects we’ve looked at. But this entire phrase describes who’s doing the action. You’ll recognise [from a previous lecture in the course] that comma as an appositive comma because A firm which specialises in corporate strategy advice refers to the same thing as we.
We also have a predicate - the part of the sentence containing the verb - in currently advise and so on.
So it would be more correct to put a full stop after TTFN, rather than a comma.
Another way of correcting the punctuation in this extract would be to replace the second comma with a full stop instead of the first comma, as in:
I am from TTFN, a firm which specialises in corporate strategy advice. We currently advise many real-estate developers across both the UK and continental Europe.
Again, we have two full sentences on each side of this full stop, and using a comma here instead of the full stop would generally be considered wrong.
In that last example, either of my suggested ways of punctuating the sentence would have been correct - it would just depend on your preference.
The only thing to remember is that if you’ve got two separate sentences, you mustn’t separate them with a comma. Instead, it’s correct to use a full stop.
This video is from my online course, Complete Punctuation: Novice to Pro, which will be published on 7 May. Subscribe below for a reminder and special introductory offer the moment the course goes live.