Commas & Structural Punctuation
Commas can be a little hard to get your head around, as a writer. They are used for many different things to structure a sentence, so unless you're thinking about that structure, you can end up with commas all over the place.
Let's go over how commas affect the structure of a sentence, and how this relates to other punctuation...
The most obvious is to indicate an "aside" as I call it. When you use two commas, like this, what is happening to the text between the commas? It's almost like using brackets (like this) to whisper something related to the sentence in the middle of it.
The comma can also mark a continuation of the sentence in a slightly new direction, tagged onto the end like this. This is similar to a colon: which adds more information to what was said so far.
However, it can also be used after the introduction to a sentence like this.
An em-dash (or long dash) can be used the same way—as an aside—in the middle or end of the sentence. It may be easier while writing to use two dashes--which are easier to type--and then go back and swap them out before printing.
"The em-dash can also be used to show something—" "Being interrupted by something else."
For example, when dialogue or narration is stopped short by some event, or another person speaking over them.
A list of items can be separated by commas such as item 1, item 2, and item 3. The comma before the final item and the "and" is called the oxford comma, after the Oxford Style' Guide's recommendation to use it. Some writers avoid that, which is recommended by the Associated Press Style. As long as it doesn't confuse the reader, you can do whatever feels natural to you.
A semi-colon is something different altogether; it joins on another complete sentence to the first that's related to it. As opposed to the colon or comma: which joins on a continuance to the sentence that's related to it.
A "full stop," or "period," leaves two sentences separate from one another. The sentences might be closely linked. They may even continue the same thought, really--like that one did.
That said, depending on your writing style or the way a character speaks, the rules about "complete sentences" can be pretty loose and casual. As long as it's not confusing, and an "incomplete sentence" continues a complete one, you should be okay.
Dialogue may contain a complete sentence, which would normally end with a full-stop. But if the sentence in general continues—with a dialogue tag indicating the speaker, for example— When a full-stop would be used at the end of a sentence as part of dialogue, but the s
"The time is six thirty-two," said the clock.
Read more about sentences here: Breaking Paragraphs and Splitting Sentences.
And an ellipsis (or "dot dot dot") lets something trail off… And maybe get picked up again later. Or to denote a pause. This is most common in dialogue, though you may choose to use it here and there in narration too if that's your style.
Just be careful to not just throw it in all over the place. A full-stop is a pause too. And a comma can be a pause. Be sure to use it when it's necessary to add to what the reader understands from the text. Use it when it adds to the story, not just any time someone takes a breath.
However, these different ways of using the comma can be confusing. The comma can be used for many things, things other punctuation can do just fine, including asides, lists, and related ideas, but also to join on new thoughts, like this. Now... how do you think that sentence was structured?
Main sentence: "The comma can be used for many things"
Aside: "things other punctuation can do just fine"
New direction: "including" a list:
"asides"
New item: "lists"
New item: "related ideas"
New direction: "but also to join on new thoughts"
Aside for the second part: "like this."
And how easy was it to figure out how it was structured as you read it? The reader doesn't know ahead of time what the structure is going to be, so they will rely on context clues to read the commas—which may be incorrect or misleading.
"The comma can be used for many things" (the main sentence). Then a comma, most commonly used to have an aside/new direction to the sentence.
"things other punctuation can do just fine". This could be an item list in theory, or maybe more likely it's an aside from the first part. This isn't completely clear, though.
"including asides". Another comma. This could end the aside and go back to the main sentence; or maybe "asides" is the first item in a list, and we're going onto a second comma.
"lists". With another comma. As that was so short, this is probably a list item, and the comma indicates it'll be followed by another item. So then "asides" was actually the first item of this list! If we guessed wrong, we've got to restructure the sentence in our minds.
"related ideas". Another comma, so this is probably going to followed by another item and the list will continue.
"but also to join on new thoughts". It doesn't really fit with the list, as this is a contradictory "but" phrase. Although this new comma could mean another item is coming, so maybe this is part of the list?
"like this." Ah, so that looks a lot like a simple aside tagged onto the previous "but" phrase. So the list wasn't continued after all.
It's kind of hard to reason about when you go word by word, comma by comma, isn't it? Your brain works fast, but it still has to do that processing. And still has to re-structure things if it went down the wrong route. This kind of thing is why sometimes you need to re-read a sentence once or twice; your brain got a bit lost in how it was structured in the first place.
This is why those other structural punctuation marks exist; to let us more explicitly structure the sentence without ambiguity. If we go full-on with using those instead, the sentence could look like this:
The comma can be used for many things (things other punctuation can do just fine), including: asides, lists, and related ideas—but also to join on new thoughts, like this.
Which can come off as more "formal" in style, as if written in a business document. But that's because it's explicit about its meaning.
And notice, I still used commas. But now, they are used within clearly marked out areas, so their meaning is clear. The one after "asides" is between the semi-colon and em-dash, and it's quite easy to see that the commas in that part are separating items. Whereas the one used before "like this" at the end is within a section between the em-dash and full-stop. And through the context you can pick up that it's a little aside.
For a more casual style, such as writing fiction, you don't need to use this explicit punctuation everywhere. Commas are just fine. Just be mindful of keeping it clear what they're doing, so the reader doesn't have to spend time and energy figuring it out.
