I mentioned in the introduction to the last chapter that some people use too many commas, while others use too few. A piece of writing that's short on commas reads breathlessly, sounds amateurish, and risks confusing the reader by creating ambiguity.
You can get away with few commas if you write mostly short, simple sentences. This puts you in the "spare" or "minimalist" style, though, and the risk is that your writing will sound dull, choppy, oversimplistic and unsophisticated. If you're aiming for an invisible style (and, again, I urge you to master invisible style before trying anything that draws attention to itself), your average sentence will be medium length--varied with shorter or longer sentences for pacing and impact--and it will require some commas.
So where do we put them? I've already mentioned several of the commonest missing commas, so let's review those before we move on.
- Use a comma before a term of address, without exception (unless for a deliberately breathless effect):
That's remarkable, Holmes!
- Use a comma after a term of address:
Watson, my bag!
- Use commas for a parenthetical statement, a self-interruption, where you could also use dashes or parentheses. (That sentence is self-illustrating.)
Actually, what I just did there is a specific kind of parenthesis called an appositive (thanks to Grammar Girl Mignon Fogarty for teaching me this). The phrase "a self-interruption" in the sentence I used in my third point is a redefinition of "a parenthetical statement," the phrase that occurs immediately before it.
If you read the Grammar Girl article, you'll learn that there are restrictive and non-restrictive forms of this, and commas are only required for the nonrestrictive one (where you're directly renaming or redescribing something that you've already named or described). This leads to one of those obscure comma rules that you don't need to worry about too much. It works this way:
My brother, Roger, lives in Australia.
My sister Jan lives in Tauranga.
Both of those sentences are correctly punctuated. The reason is that I only have one brother, so "my brother" and "Roger" are the same person (it's a nonrestrictive appositive, a direct renaming). However, I have two sisters, so "Jan" is a restrictive appositive--it clarifies which sister I'm talking about.
Very few people know this rule, so if you mess it up hardly anyone will care. The important point is this: if you use a name or description for someone or something, and then immediately afterwards use another name or description, separate them with a comma. More examples:
You're going to Hogwarts, a famous school of witchcraft and wizardry.
I spoke today to Henrietta Wibsley, the world's most prominent aardvark.
Commas are used to separate lists:
I bought celery, capers, and aardvark treats.
What I've just demonstrated is called the "Oxford comma," and it's controversial among people who care about commas (who need to get a life, yes, I know). Some say that, since it makes lists less ambiguous sometimes, it should be used all the time. Others disagree.
The Oxford comma is specifically the last comma in the list. Here's a famous example (from an actual newspaper account of a documentary on Merle Haggard):
Among those interviewed were his two ex-wives, Kris Kristofferson and Robert Duvall.
The problem comes because that's a list, but it reads like an appositive (as if "Kris Kristofferson and Robert Duvall" acts as a redescription of "his two ex-wives"). With the Oxford comma, it's clear that it's a list:
Among those interviewed were his two ex-wives, Kris Kristofferson, and Robert Duvall.
In the list "celery, capers and aardvark treats," all three are clearly grocery items, equal members of a list, and so it's just as clear with or without the final comma.
Whether or not to use the Oxford comma is a style choice, unless the sentence is ambiguous without it. Personally, I tend to use it all the time in case I don't notice an ambiguity, and because consistency is good.
It's still possible to be ambiguous even with the Oxford comma, of course, if something in your list sounds like it could be an appositive for something else. Mignon Fogarty cites "I went to see Zach, an officer, and a gentleman," which could be three people or two (if Zach is an officer). Stay alert to this, and rewrite if necessary.
Mo' Info, Mo' Commas
Appositives are only one example of parenthetical commas that change the meaning of a sentence. There's a broader category of phrases that add information to the sentence, even if they don't rename or redescribe the phrase they follow. For example:
The aardvarks who were present cheered.
The aardvarks, who were present, cheered.
Those two sentences mean two different things. In the first, "the aardvarks who were present" are being, by implication, contrasted with "the aardvarks who were absent". In the second, "who were present" gives us more information about the aardvarks, and why we're mentioning that they cheered. If you're giving the reader more information, show this by giving them more commas.
Nor is this the only kind of phrase that's set off by commas. Transitional adverbs like however or therefore or in addition, especially when they come at the start or end of a sentence, get commas:
Therefore, I propose that we kill the Batman.
The aardvark didn't notice, however.
Modifiers, and How Not to Dangle Them
I've left this one until last, because there's a pitfall I want to explore.
Modifiers are phrases like "making me wonder what had happened," which give more context to the rest of the sentence. They can come at the start or the end of the sentence. They need to be set off with commas:
Henrietta burst through the aardvark door, making me wonder what had happened.
Seizing my opportunity, I pocketed the jade bracelet.
Modifiers carry a risk. The author Jim Butcher's Wikipedia entry used to have a sentence that started out this way:
While sick with strep throat as a child, Butcher's sisters introduced him to The Lord of the Rings.
Taking advantage of Wikipedia's policy of allowing anyone to edit, I corrected this. (That last sentence also has a modifier. Did you notice?)
Can you see what's wrong with the original version of the sentence? Think through its literal meaning.
The person who originally typed that sentence presumably had a thought process that, if it had been more explicit, would have run something like this: Jim Butcher is the subject of this article, so any sentence in it is implicitly about him. However, what the sentence literally said was that his sisters were ill with strep throat when they introduced him to The Lord of the Rings. Here's my correction:
While he was sick with strep throat as a child, Butcher's sisters...
You'll sometimes see this kind of structure discussed under the heading of "dangling participles" or "misrelated participles". Strictly speaking, since there is no "-ing" or "-ed" form in the phrase "while he was sick with strep throat as a child," it isn't a participle, so I'm using the term "modifier" as a more general description.
I recently read a book that had multiple dangling modifiers, including these (slightly altered to disguise their origin--though I read a pre-publication version, so hopefully someone found and fixed them):
Pressed against the wall, a sick dread filled him. After cycling open, the air smelled old. Plunging through an arch, the curvature of the planet was revealed. Pushing a hand into the interface, the grid welcomed her.
In all these cases, there's an implied subject that's different from the grammatical subject of the sentence. In the first case, "he" is the implied subject, and is doing the action described by the modifier ("pressing against the wall"), but the grammatical subject of the sentence is "a sick dread". In the second, the implied subject comes from a previous sentence which mentioned an airlock, which is what is cycling open, but the grammatical subject is "the air".
There's an easy fix for these, and it's to mention the intended subject explicitly. Like this:
As he pressed against the wall, a sick dread filled him.
After the airlock cycled open, the air smelled old.
As the ship plunged through an arch, the curvature of the planet was revealed.
She pushed a hand into the interface, and the grid welcomed her.
Dangling modifiers show fuzzy thinking and, besides leading to unintentionally ridiculous scenarios, reduce the reader's confidence in you as a writer. If you let your modifiers dangle, you'll trip over them and fall on your face.