Commas are a slippery piece of punctuation. Because there are some cases where commas are optional, many editors believe that the comma is a much more flexible piece of punctuation than it actually is. Our subject matter — which includes a lot of fictional alien names — makes the use of commas in some situations compulsory, even though such usage would be optional in other contexts.
After a form of address
If you're talking to someone, and you say their name or title, you should place a comma after their name.
- Correct: Doctor, come here.
- Incorrect: Doctor come here.
After a general noun that immediately precedes a more specific example of that noun
This usage of commas is really very important on a wiki like ours, which includes a lot of weird species names. However, it's something that's often ignored or just not well-understood. Consider this sentence:
- Barbara was concerned about her student, Susan.
The comma before Susan is actually compulsory. If it's left out, many of us would still be able to make sense of the sentence, because we understand what a student is, and Susan is a very common first name. But leaving off the comma is still, technically, wrong. The reason for this becomes clearer when we start using less familiar words:
- Sarah Jane once fought against Qetesh Ruby White.
- Sarah Jane once fought against Qetesh, Ruby White.
The comma here makes all the difference. Without the comma, a valid reading of the sentence is that Qetesh is a title, as in President James Buchanan. With a comma, Ruby White is clearly a part of whatever group is described by the noun Qetesh.
Since races are often blue-linked next to individuals of that species, it's very important to include a comma between the race and the individual to tell the reader that the race name is not a title, or that the whole thing, "Qetesh Ruby White", isn't a single, triple-named entity. Remember, you, as an editor on a Doctor Who wiki, might not even blink at the lack of a comma, because you know what a Qetesh is and who Ruby White is. However, the casual reader, or even the Doctor Who fan who simply has never seen SJA, probably won't parse those three words correctly without a comma.
Here are some other correct examples of comma usage of this case:
- Martha Jones loved the film, Breakfast at Tiffany's.
- The Eighth Doctor wasn't a fan of the television series, Babylon 5.
- The Third Doctor once placated the great beast, Aggedor, with a lullaby.
- Ben Jackson was a seaman on the naval vessel, HMS Teazer.
- The only on-screen writing credit for Donald Tosh was for the fourth episode of The Massacre, "Bell of Doom".
In a list
Commas separate items in lists, as in the sentence: "The Doctor has a recorder, a frilly shirt, a scarf and a bowtie." Note that a comma before the conjunction, and, is optional, but generally avoided. It's thus correct, but somewhat antiquated, to say, "The Doctor has a recorder, a frilly shirt, a scarf, and a bowtie."
Independent clause separation
Commas are used to separate two clauses in a sentence which are independent of each other. That is, the two clauses could easily form sentences of their own.
- Correct: The Doctor browbeat the Dalek, but Martha chose a less confrontational approach.
- Incorrect: The Doctor browbeat the Dalek but Martha chose a less confrontational approach.
When you have two complete clauses, both with their own subjects and verbs, you should put a comma at the conjunction. Note what happens when the second clause is turned into a dependent clause:
- Correct: The Doctor browbeat the Dalek while humming a merry tune.
- Incorrect: The Doctor browbeat the Dalek, while humming a merry tune.
The comma is wrong here, because "humming a merry tune" is a dependent clause that has no subject and only a participle for a verb.
Far more common than "while" are the conjunctions "and", "but", "or" and "yet". A comma should go before any of these if the clause that follows has a subject and a verb.
- Correct: Jo would have stayed with the Doctor, but she got married.
- Correct: Sarah Jane could either keep to herself, or she could invite Maria into her life.
- Correct: The Tenth Doctor saved the universe from Rassilon's plan, yet he still died for Wilf.
- Correct: Nyssa solved the mathematical equation, and Tegan explored outside the TARDIS for any signs of 20th century Earth.
- Incorrect: Jo would have stayed with the Doctor, but got married instead.
- Incorrect: Nyssa solved the mathematical equation, and explored outside the TARDIS for any signs of 20th century Earth.
Commas are required in some cases before a direct quotation, typically when you are quoting a full sentence. Semi-colons may not be substituted for a comma in this case. Commas are entirely disallowed prior to a sentence fragment.
- Correct: Roz called Chris "embarrassing, dumb and misplaced".
- Correct: The Doctor said to Jo, "That's a most good-humoured wine."
- Incorrect: The Cybermen called the Doctor, "Inefficient".
- Incorrect: Sarah said "Don't forget me."
- Incorrect: The Daleks seemed uninterested in their prey, failing even to inflect when they said; "Exterminate."
Using commas where a full stop or conjunction is required
Commas have precise meanings. They can't just be used wherever one wants in a sentence. One of the biggest problems associated with comma use is when a comma is used to continue adding thoughts to a sentence.
- Incorrect: Jo claimed to be a qualified agent, she may have exaggerated about this in the same way she exaggerated the extent of her A-Levels.
This is incorrect because there's no conjunction present. Thus, there are at least two ways to improve the punctuation of this thought. Proper punctuation demands one either break up the thought into two sentences or place a conjunction after the comma:
- Correct: Jo claimed to be a qualified agent. She may have exaggerated about this in the same way she exaggerated the extent of her A-Levels.
- Correct: Jo claimed to be a qualified agent, but she may have exaggerated about this in the same way she exaggerated the extent of her A-Levels.
Additional help with commas
You can find more help in a detailed exploration of comma usage at Talk:Jo Grant#Excessive commas?