A writing teacher will generally tell you to use parentheses very sparingly. I agree. When overused, they 1) become an annoying tic and 2) can lead you to include stuff that you’d be better off cutting. But that’s not to say they aren’t mighty useful at times. It’s definitely worth mastering them, thereby enlarging your punctuation arsenal.

Parentheses = Invisibility Cloak

When you use a set of parentheses, you’re cordoning off its contents from the rest of the sentence. Whatever’s inside those parentheses becomes invisible to the main sentence’s syntax and punctuation. Writers run into problems when they don’t follow that rule. Here’s an example of incomplete invisibility:

Luckily, his pet crow, (which I call Poe), caws loudly to let me know when he’s around.

If the stuff inside parentheses is invisible to the main sentence, you should be able to pluck the whole parenthetical aside out without having to make any changes to the sentence’s syntax or punctuation. But when you try that with the example I’ve just quoted, this is what you get:

Luckily, his pet crow,, caws loudly to let me know when he’s around.

Two commas in a row can’t be right, so the punctuation surrounding the parenthetical aside must’ve been incorrect. In fact, the writer was treating the phrase “which I call Poe” as though it were part of the main sentence, not separated out by parentheses. Here’s how it should look:

Luckily, his pet crow (which I call Poe) caws loudly to let me know when he’s around.

When writers make punctuation errors within parentheses, it’s also often because invisibility is not being maintained. Such an error might look like this:

Luckily, his pet crow, (which I call Poe,) caws loudly to let me know when he’s around.

When you do the plucking-out test, here, you lose one comma but not the other:

Luckily, his pet crow, caws loudly to let me know when he’s around.

No way should there be a comma in that spot. The error reveals that, once again, invisibility is not being maintained. The writer is punctuating in and around the parenthetical aside as though it were part of the main sentence.

Commas = Sheep Dogs

Another error I see has to do with grouping. When it comes to parenthetical asides, commas and periods are sort of like sheep dogs: they “herd” the aside into the right part of the sentence. Here’s an example of “comma-herding” gone wrong:

After Saran-wrapping the latest condiment-shelf concoction, I crammed it between the others I’d created over the past few nights: a bologna and apple jelly sandwich, (eew!) a Swiss cheese and tartar sauce sandwich, (blah!) and a peanut butter, mustard, and pickle relish sandwich.

In the above sentence,  the “(eew!)” aside goes with “a bologna and apple jelly sandwich,” not “a Swiss cheese and tartar sauce sandwich,” but the comma has grouped the “(eew!)” with the latter. The same thing is happening with “(blah!)” — it should go with “a Swiss cheese and tartar sauce sandwich,” but the comma has grouped it with “a peanut butter, mustard, and pickle relish sandwich.” Here’s how the sentence should look:

After Saran-wrapping the latest condiment-shelf concoction, I crammed it between the others I’d created over the past few nights: a bologna and apple jelly sandwich (eew!); a Swiss cheese and tartar sauce sandwich (blah!); and a peanut butter, mustard, and pickle relish sandwich.

(Want to know why I’ve replaced the commas with semicolons? See my Mechanics Moment on semicolons and complex lists.)

When a parenthetical aside appears at the end of a sentence, you have to decide whether it should stand alone as its own independent clause (in which case there has to be a complete sentence within the parentheses) or be included within the main sentence. If it really is part of the sentence, the period needs to herd it into the sentence, rather than leaving it stranded. Here’s a stranded aside:

I can only see Grandpa Edgar and Kyle, and that’s because they still have work to do on this side. (helping yours truly)

It should be punctuated thus:

I can only see Grandpa Edgar and Kyle, and that’s because they still have work to do on this side (helping yours truly).

In contrast, an aside that stands as a real independent clause should be outside the main sentence’s period and should have an internal period as well:

I didn’t like pastrami or pimento cheese, so I knew I’d been influenced by some new visiting kid. (I’m a plain ole peanut-butter-and-jelly-with-Fritos-on-the-side kind of girl.)

English is a compulsive eater. It grabs words from other languages and … sluuuuuurp! … swallows them right down. That means we have a number of terms that don’t operate according to the usual English pattern of marking the plural with a terminal “s.” Most such words are from Greek and Latin. Once you get a feel for how they work, they fall into place. So, okay, say it with me:

One index, two indices.

One phenomenon, two phenomena.

One datum, two data.

One medium, two media.

One criterion, two criteria.

One antenna, two antennae.

One cherub, two cherubim.

One thesis, two theses.

One colloquium, two colloquia.

And so forth. There are dozens. On the other hand, some of these words have been Anglicized to the degree that an English-style plural is at least an option. Yes, you can have “two octopi,” but you don’t have to: “two octopuses” is fine. And as I recall, a few years ago The New York Times dumped “millennia” in favor of “milleniums.” That one still jars, for me, but oh well.

In my last MM, I talked about using semicolons as “softer periods” to join two sentences into one. That’s the main use of this mark of punctuation, but there’s another instance in which you’ll see it: the complex list. This use of the semicolon is unrelated to its main function.

Here’s a simple list:

Fred went to the store and bought milk, eggs, and cat food.

It’s pretty easy to figure out the items in this list, as they’re separated from one another with commas:

A = “milk”
B = “eggs”
C = “cat food”

But what if A, B, and C are longer and more complex? What if you get lists within your lists?

Joe Doe is survived by his wife, Nancy Smith, his sister Samantha, his three sons, Paul, Edward, and James, his daughter, Jane, six grandchildren, Sally, Janine, Robert, John, Peter, and Frank, and one great-grandchild.

A complex list is a list in which at least one individual item contains a comma. For instance, in the above sentence, C = “his three sons, Paul, Edward, and James.” The commas that separate C from B and D blend together with the commas inside C. That makes the above sentence pretty hard on a reader: she can’t tell immediately where C begins and ends. Instead, she has to read slowly, grouping the names into categories as she goes. The point of punctuation is to make things easier for your reader. In the above sentence, punctuation is not going its job.

Semicolons clarify complex lists by replacing the commas between items. Here’s what the above sentence looks like when punctuated correctly:

Joe Doe is survived by his wife, Nancy Smith; his sister Samantha; his three sons, Paul, Edward, and James; this daughter, Jane; six grandchildren, Sally, Janine, Robert, John, Peter, and Frank; and one great-grandchild.

Having even one item with one internal comma is enough to trigger complex-list punctuation, but if you don’t have at least three items, you don’t have a list:

Fred went to the store and bought milk and a bunch of pet supplies, including cat food and bird seed.

“Milk” and “pet supplies” aren’t a list, and “cat food” and “bird seed” aren’t a list, either. Only when you get three or more items to you have to start thinking about list-punctuation issues.

My last MM (mechanics moment) focused on colons. Now we’re moving on to semicolons, perhaps the most often misused mark of punctuation in English.

Colons and semicolons look similar, so people tend to get them confused. That’s unfortunate, as they work in very different ways: whereas colons separate general and more specific segments of a sentence, semicolons separate two independent clauses within a single sentence.

An “independent clause” is a statement that could stand alone as a complete a sentence. How can you tell you have one? Easy: you have a subject and a verb. “I walked” is an independent clause, even though it’s short.

So, why would you want to put two independent clauses in one sentence? In general, you’d do it to show that the two clauses are closely related in terms of logic. Maybe they’re cause and effect. Maybe they’re fact and reinforcement. Maybe they’re point and counterpoint. Here are some examples:

1. Joe lay in bed, thinking about how bad his day was going to be. It was Monday, so all the new reports would be landing on his desk; moreover, the boss had scheduled a staff meeting.
2. Joe’s boss was prone to logorrhea; however, that day he was strangely silent.
3. Maybe he had laryngitis; maybe someone’d finally cut out his tongue.

Notice that none of the above situations have that general-to-specific structure we saw with colons.

Often a semicolon is followed by what my ninth-grade teacher called a “flow word” — “however,” “for instance,” “moreover,” “for example,” etc. Flow words help your reader immediately understand how the two halves of the sentence relate to one another. That’s a kindness, but it’s not required, and in some kinds of writing it would probably sound stilted.

What is required is that you have an independent clause on both sides of the semicolon. This rule is non-negotiable. Semicolons allow you to combine two complete sentences into one. They replace a period, not a comma. This mistake is the one I see over and over again: a semicolon with a fragment on one side or the other. I think some people think of the semicolon as a “stronger comma.” It’s not. It’s a “softer period.”

You wouldn’t use a semicolon to introduce a quote or a list (you’d use a colon):

Joe lay in bed, thinking about how bad his day was going to be: a dozen new reports, an interminable staff meeting, sixty-three paper jams, and Sally’s overpowering perfume.

You also can’t use multiple semicolons in one sentence, except in the case of complex lists. See Semicolons, Part 2, for a discussion of that very different use of the semicolon.