I occasionally proofread texts, and adding missing commas probably takes up half of my time. Removing superfluous ones is a smaller issue, but it’s a close contender. The third, if anyone is interested, is surely missing hyphens in compound adjectives. So, this will be a post about commas and, since they are related, semi-colons. However, the goal is not to remember any list of 8, 10, or 17 seemingly arbitrary rules but to understand the underlying logic, which exists.

So, let’s start with the basics. I don’t care about what your teacher taught you when you were a kid; commas do not represent pauses, and periods are not longer pauses. Commas are not typographical signs that indicate any breaks—well, at least, that’s not their primary function. They happen to be used in situations when, usually, a pause may be used, but not always, and certainly not as a mandatory thing to do. And, most importantly, if when speaking you pause somewhere, that doesn’t mean that when that is translated into text, there should be a comma. Lists are a clear example of why the two things are not the same:

“I’m off to the store to buy some basic items: paper towels, hand sanitizer, and punji sticks for the neighbors.”

If you were to read that out, there would be no significant pause between the items of the list, and it would not sound faster than “paper towels hand sanitizer and punji sticks” if such were the way to write lists in modern English.

The commas are there just to separate items and avoid confusion, such as believing I’m going to buy paper and towels. Unlikely to happen at this level of simple sentence, perhaps, but commas make everything tidier, and once sentences become humongous, paragraph-long beasts, they are a great help.

I mention all of this because it became clear to me that the reason I have to keep marking up missing commas is that many writers just hear the sentences in their minds, see no meaningful pause, and so they say to themselves, ‘Pff, who needs a comma here?’ That would be OK if the function of a comma were to mark the moment when you hold your breath, but it’s not. And in case you are wondering what to use to signify such a pause or break, well, you can always use — or ….

“But—no, this cannot be!” rather than “But, no, this cannot be!”

Again, this is important because if you don’t understand comma placement, that means you probably don’t understand what a sentence is either. Not to a master level anyway. And the sentence (not the word) is the fundamental unit of thought in writing.

So, I will start with an elementary sentence, and build up from there so you can see the underlying logic as it grows from the basic seed:

The cat eats the mouse.

This is a simple, main clause than forms an entire sentence. It has a subject (the cat) and the predicate, which includes the verb (eat) and the direct object (the mouse.)

Nobody in his right mind would write The cat eats, the mouse. Now, look at this:

The cat eats the mouse and runs away.

Is this correct… or incorrect? And why? I think that most people would say correct, but I have fixed enough sentences like The cat eats the mouse, and runs away, to know that a lot of you get confused at this stage.

But what about this: The cat eats the mouse and the dog.

That one is simpler since I’m sure fewer people would write The cat eats the mouse, and the dog, and those who did so would be, most likely, doing so to imply some dramatic contrast or surprise (but that’s not what commas are for.)

Let’s build the entire list from the beginning to see the underlying logic better as it grows:

The cat ate the mouse.
Subject -> Verb:DirectObject
The cat ate the mouse and ran away. (that’s 2 actions & 1 subject)
Subject -> (Verb:DO & Verb)
The cat ate the mouse and the dog.
Subject -> (Verb:(DO + DO))
The cat and the mouse ate the dog and ran away.
(Subject & Subject) -> (Verb:DO & Verb)
The cat and the mouse ate the dog and the bird and ran away.
(Subject & Subject) -> (Verb:(DO + DO) & Verb)

Now, you may be looking weirdly at the last sentence, and I don’t blame you, but I assure you it’s correct (although ugly.) It’s just saying that Two animals ate two things and ran away. But look at what happens if I change a little thing:

The cat and the mouse ate the dog, and the bird ran away. (Yes, the bird is running, not flying.)

Now the underlying grammar looks like this:

(Subject + Subject) -> (Verb::DO) // Subject -> Verb

The comma represents that // a cut but also a link between the two independent clauses (and they are called independent because they can stand on their own like independent sentences.)

Basically, commas work like mathematical parentheses; they keep like things together and things that shouldn’t go together separated. And the most fundamental rule that people keep ignoring is that different subjects that do different things need a comma between them. In the two sentences above, the first one states that the mouse and the cat (that’s the subject) eat two creatures and then run away. The subject is the same, so no comma is needed. Another example:

My father writes and paints and sings and dances and cooks.

That is perfectly valid, although, of course, you could make it a list: My father writes, paints, sings, dances, and cooks.

But when another subject (even if a pronoun referencing the same, previous subject) appears, things change. See, again:

The cat and the mouse ate the dog, and the bird flew away.

This could have been written as two independent sentences: The cat and the mouse ate the dog. The bird flew away. But it’s kind of boring and fails to imply the connection between the two actions.

Why is this important? Mostly to avoid ambiguity. If I start reading a sentence that goes like The cat eats the mouse and the bird… I would naturally assume two things are being eaten here, but if then it changes to …the bird runs away (without a comma in between,) my brain has to go back to the start to reclassify this as two separate actions by two separate entities. Because these two could stand as separate sentences, with a full stop between them, if you want them together as a single sentence, you need to link them with a comma and a conjunction. This conjunction could be any of the known FANBOYS:

For

And

Nor

But

Or

Yet

So

But, and this is very important, the comma is not there because this arbitrary mnemonic says so but because of their grammatical function. If these conjunctions are not coordinating distinct clauses, then the comma is not needed:

The bird doesn’t fly but runs.

The bird doesn’t fly, but the cat does.

Two separate subjects, two separate verbs, two separate clauses. Therefore, a comma. Keep in mind that this applies even when the new subject refers to the same entity:

The cat eats the mouse and it runs away (NO, even if “it” could be the same cat—not that wecould know)

The cat eats the mouse, and it runs away (YES, but ambiguous and not a very good sentence.)

The reason becomes clear if the pronoun it is replaced by the thing being referenced: The cat eats the mouse and the cat runs away. That still creates the same problem mentioned before. Is the cat eating the mouse and… another cat? Oh, wait, no. But it’s the same cat, or another? And so on.

However, if you remove the pronoun, there’s no confusion and no need for a comma: The cat eats the mouse and runs away. So, here’s a tip, if the same subject is doing many things, you can (or even should) remove the repeating subject/pronoun.

If commas are used in some of the previous sentences but not in some of the others, it’s not because you pause in one but not the other but because they tell you who is doing what. How to read them is up to you. Again, they work sort of like parentheses showing the grammatical relationships between clauses and their components:

(The cat tries to eat the mouse), and (the bird runs away.)

Which is different from:

(The cat tries to eat the mouse and the bird)

If you have understood what I have said up until here, then you will avoid half of the mistakes I have to fix. Moreso, you have the knowledge to understand semi-colons and more complex sentences. Again, let’s start with simple ones and build up from there. Here we have two related sentences:

The cat loves to eat mice. They are fun to hunt.

That’s fine, but unless you are going for a creepy, serial killer with a primary-school-level-of-writing vibe, this is lame. These are just two lonely sentences. However, there are many ways to link them. The easiest way is to add because:

The cat loves to eat mice because they are fun to hunt.

But should that have a comma before the because? The answer is no, and, once again, the reason goes back to what can stand on its own. Because they are fun to hunt cannot stand alone; your brain demands to know more. It’s not a complete thought; something is missing. On the other hand, The cat loves to eat mice is a fine sentence and works as a unit of thought. If you invert the sentence, however…

Because they are fun to hunt, the cat loves to eat mice.

Then you need a comma. You know when the dependant with Because… starts but not necessarily when it ends, so you need a comma. This is easier to see with this example:

Cats eat mice because it is fun to hunt.

The because already tells you that whatever follows (it is fun to hunt) needs what came before, so there’s no difficulty in reading and understanding the sentence, but if you switch it:

Because it is fun to hunt cats eat mice.

Without a comma, your brain will first interpret this as something about hunting cats… and that you should eat mice? So put a comma in there, and the problem is fixed. To repeat, it’s not about any “pause” but to define the limits and grammar of your sentence and its parts so that it’s clear who or what is the subject and who does what.

Now, with that said, you can understand the first function of the semi-colon, which is to join independent clauses like a period, but with the strength and psychological effect of a comma. So:

The cat loves to eat mice. They are fun to hunt. (YES)

The cat loves to eat mice, they are fun to hunt. (NO, you need a coordinating conjunction)

The cat loves to eat mice, and they are fun to hunt. (YES)

The cat loves to eat mice; they are fun to hunt. (YES)

The cat loves to eat mice; and they are fun to hunt. (NO, a comma would be enough.)

The semi-colon is especially useful (and that’s the reason it was first invented) to contrast related but independent clauses:

The cat killed only the mice; all the other animals had already fled.

This could have been written as two separate sentences with a period, and there would be nothing wrong with that, but the semi-colon gives you a stronger sense of the interrelationship between the two. Personally, though, I would just write “because…”, but I mention this, so you know there are many options for writing the “same” idea.

Using a comma instead of a semi-colon in the sentence above, although a common thing even in professionally edited writing, is incorrect. Again, a comma without a coordinating conjunction cannot link two independent clauses. It’s not its function, and it has nothing to do with how long you pause or hold your breath or if you want to make your writing “fast” or “slow” or whatever strange justifications one can read.

The second and final function of a semi-colon is a sort of comma of commas, or “super comma,” but it still follows the same logic of like things going together I mentioned before. It is used when you have a list where at least one of the items also employs a comma. So, for example:

When the Cat went hunting, he caught the Mouse and the Bird and the Squirrel.

That is simple and straightforward, and it doesn’t even need commas because I use and instead. However, imagine that we wanted to say something about each of those three items. Using only commas (or worse, no commas between the items) we might end up with something like this:

When the Cat went hunting, he caught the Mouse, a small, brown creature, the smallest of the animals of the forest, who many times had hidden from the cat by scurrying under the roots of a tree, and the Bird, the fleeting, colorful singer of those lands, and, finally, the Squirrel, the most diligent being a mile around.

That’s… not good. I mean, you can understand it, but it’s not easy reading. The more commas you keep adding, the more likely you are going to screw up somewhere, and a not very attentive reader might think the Mouse hid under the roots of the tree and the Bird. Semi-colons help in such situations:

When the Cat went hunting, he caught the Mouse, a small, brown creature, the smallest of the animals of the forest, who many times had hidden from the cat by scurrying under the roots of a tree; then the Bird, the fleeting, colorful singer of those lands; and, finally, the Squirrel, the most diligent being a mile around.

As I said, it is sort of a comma of commas, like nested parentheses. It’s useful when you want to list things but also explain something about each item. Since most writers don’t know how to use the semi-colon correctly when faced with such a dilemma, they have to do something like:

When the Cat went hunting, he first caught the Mouse. [Sentences describing the Mouse.] He also caught the Bird. [Sentence explaining the Bird] Finally, he caught the Squirrel, who was such and such.

That’s OK, but it can break the flow. You can, however, condense all that information into a single, flowing, cumulative sentence. Not that I have ever personally proofread any text that did such a thing, but the option is there if you want to try new things or, indeed, show off a bit.

And these are the two uses of the semi-colon; there aren’t more as far as I know. So now you know the mystery of the ;

What else? Where, with that and common sense, you can probably get 80% of all commas right. But there are a few extra situations I will mention to bump that to 95%

Introductory clauses: Just put a comma there. Don’t even think about it. Again, it’s not about sound or pause. See? I put a comma after again; I didn’t even think about it. Sure, there might be some situation, especially if the sentence or phrase is really short or it’s informal writing, when you might try something else, but the safest bet is just to write the comma:

However, I…

When all is said and done, the…

After the sun went down, we…

Etc. Introductory? Comma.

Adjectives: When more than one adjective precedes a noun, sometimes these will have commas in between but sometimes not. The exact reason is a bit convoluted and hard to explain, but the general logic is that similar (on the same “level” or “type”) adjectives need a comma, but different ones do not. So, you write A large French stone building (three different descriptive adjectives of size, origin, and material), but you write An ugly, repugnant creature (two “opinion” adjectives.) How to know for sure? Switch or alter the order of the adjectives and try to separate them with the conjunction and. If it still makes sense, then you need a comma; otherwise, you don’t.

A French and stone large building (wat?)

A repugnant and ugly creature (it still makes sense.)

In my experience, that works almost always.

Parenthetic expression: I have compared the use of commas to parentheses, so it goes without saying that anything that has a parenthetic function would use them. Without getting dirty with the specifics, by that I mean any expression that, well, pretty much seems to be between parentheses. These can be short:

“The man, whom I did not recognize, arrived.”

Or a disgusting, bloated monstrosity:

“The man, not the winsome one poor Ophelia had been waiting for but the rascal about whom Lady Rowena had warned us many times because she feared he would be the ruin of our family and estate, arrived.”

And, naturally, there can be one, two, three, and as many as you want of those. Do not get all mixed up with that/which, though. That, when used as a relative pronoun, defines a subset of something, but it is not “parenthetic” as I’m using it here.

Everything that sparkles is not gold

is fine. On the other hand:

Everything, which sparkles, is not gold

sounds like an LSD-induced sentence. Another example:

Cats that purr are happy. This is saying that, of the set of cats, the subset that purrs are happy (this doesn’t imply that those who don’t are unhappy btw.)

Cats, which purr, are happy. This is saying that all cats are happy, and they also happen to purr (and it’s implied there’s some link between the two things.)

So, with all that said, you should get most of your important commas right. You might miss some, but it’s not as if anybody really cares that much about this anyway. And, finally, if none of these explanations apply and if common sense fails, then yes, try to think of the comma as a pause and see if it fits. But that should be the last resort strategy.

There you go. With this, you’ll write a bit better, and you’ll make my job easier too. After all, I get paid the same whether I have to fix 1000 or 5 errors in a text.