So, this is grammar, right? Every pedant knows that there is a right way and a wrong way to do everything, and the comma cannot be an exception. Right?
Frustratingly for all our inner (and occasionally outer) pedants, it is not quite as black and white as that. Many of the rules about the use of the comma are quite strict and immovable, but others are a little greyer, a little more yielding. It often comes down to personal taste or corporate and institutional styles. Let’s look at the comma rules.
Commas between subjects and verbs
Here’s a clear comma rule to get us started. Do not put a comma between the subject of a sentence and its verb. For example, Thursday afternoon, is my favourite time of the week would be incorrect any day of the week, and simply looks as though someone leaned on the keyboard while reaching for a bottle of water.
It doesn’t matter how long the subject of the sentence is (i.e. the words that are ‘doing’ the verb), or how much of a pause you might leave if you were reading the sentence out loud, commas are forbidden in between subject and verb. A longer sentence example would look a bit like this:
The smell of Agent Orange wafting over the Orinoco river that dusky evening, was never going to leave her nostrils.
And speaking of pausing while speaking…
Don’t add a comma when you would pause
Punctuation may have originally been used to show the person reading aloud where on the page they should pause for breath or dramatic effect, but that role has long been made redundant.
Writers can panic when confronted with a long sentence, and the temptation to scatter a fistful of random commas over a particularly difficult-to-digest paragraph can be very powerful. But take a deep breath (real or imagined) and remember that in recent times commas are only really used when necessary. Less is often more.
Commas and apposites
A comma can also be used as a virtual equals-sign in a way that often appeals to marketing people and writers that like snappy mottos. For example:
Learning commas, learning communication
This use of the comma is more flexible than using colons, which sometimes play a slightly similar role, and so would appeal more to writers looking to suggest qualities rather than try to state them concretely.
This effect is also used more mundanely to add extra description. For example, My brother John lives in Wales specifies my brother by name, suggesting I may have other brothers, maybe even living elsewhere; however, My brother, John, lives in Wales points out that in fact I have only the one brother, adding his name for extra (technically unnecessary) detail.
Once again, the mighty comma carries a soft stick, pointing out differences that might not even be obvious when the phrase is spoken aloud.
Comma as apposite in fiction
The more flowery language tries to become, the more it will draw on commas to allow this extra information to be added into a sentence. Fiction is full of such commas, enabling the writer to fulfill their literary ambitions, to riff and riff again until the weary reader begs them to stop, to keep stacking more and more clauses onto their sentence until it creaks with the weight.
(Did you see what I did there?)
More correctly, apposites refer normally to nouns or noun phrases, but the effect is very much the same, the same buttons are pushed, the boxes ticked as you might expect.
Comma or semi-colon
Finally, we can look at the differences between the use of commas and semi-colons. This is a nice, simple one.
There are two main areas where semi-colons are used: to join together independent phrases into a single sentence; and marking out items on a list that begins with a colon, as you can see here.
Commas can also fulfill these roles, but need to use conjunctions to help tie the phrases together.
Examples of commas and semi-colons
I took my dog to the vets, but there was nothing they could do.
as opposed to
I took my dog to the vets; there was nothing they could do.
The choice between them is purely a stylistic one. The semi-colon could as easily be replaced by a full stop and the second clause form a new sentence.
Commas or semi-colons in lists
Again, one of the primary roles of the comma is to separate items in a list. However, if the items on the list are a little too wordy to be easily navigated, then the semi-colon can help. This is especially useful if the item itself features commas.
An example of a semi-colon list
The advantages of the plan were manifold: the smell of turpentine would not be a factor, which Jasper was relieved about; the money would be far easier to distribute around the underground, which was very important; and she had always preferred that colour.
What about using commas in the context of a clause that states a definition? For example, “The old fashioned computer monitor, or cathode ray tube, became obsolete with the advent of the LED monitor.” What do you call this and is my example correct?