Here are discussions of seven types of situations in which the presence or absence of a comma depends on various factors.
1. Word Function
Whether a comma follows a word sometimes depends on the function of the word. For example, when now is employed at the head of a sentence to refer to the present time, there’s no reason to separate it from the rest of the statement: “Now you know.”
But when now serves as an interjection to mark a transition or attract someone’s attention, it should be set off: “Now, have you had dinner?” (That same series of words could be used in a temporal sense, though: “Now have you had dinner?” suggests that the writer is impatient with the person the question is directed to.)
2. Before Because
A sentence such as “I didn’t want to go because I hadn’t enjoyed myself last time” implies that the writer is explaining that the lack of enjoyment isn’t a factor in reluctance to attend an event; the reason for the reluctance will presumably follow.
But if the meaning is opposite — if the lack of enjoyment is the reason for the reluctance to attend — a comma should precede because to signal that what follows the comma is a dependent clause: “I didn’t want to go, because I hadn’t enjoyed myself last time” Alternatively, the dependent clause can begin the sentence: “Because I hadn’t enjoyed myself last time, I didn’t want to go.”
3. Apposition
An appositive is a word or phrase equivalent in meaning to an adjacent word or phrase, as in “She wrote to her brother, John”; “her brother” and “John” mean the same thing, so they are appositives, and the comma is necessary to set it off. However, if the woman has more than one brother, write “She wrote to her brother John.”
Similarly, in “I met the writer, Jane Doe,” the comma is correct only if the writer has been alluded to before without mention of her name. Otherwise, the comma between the appositives suggests that only one writer exists. (And that puts me out of a job.) Even if writer is modified, the meaning differs: “I met the mystery writer, Jane Doe” suggests a previous reference to two or more writers, only one of whom writes mysteries, whereas “I met the mystery writer Jane Doe” simply specifies the genre in which Jane Doe writes.
4. Relative Clauses
Commas may or may not be necessary, depending on whether each statement in an otherwise identical pair of sentences uses the word that or which: In “The house that Jack built is falling apart,” the phrase “that Jack built” is essential to the sentence, which specifies a particular house. In “The house, which Jack built, is falling apart,” the emphasis is on what is happening to the house, and the identity of the builder is a parenthetical, so the optional information should be bracketed by commas.
“The house which Jack built is falling apart,” without commas, is also correct; it is identical in meaning to “The house that Jack built is falling apart.” However, the convention in American English is to avoid using which in this sense to prevent confusion with the meaning of the sentence with the parenthetical phrase.
5. Short Introductory Phrases
Many people choose to omit a comma after introductory phrases of just a few words, as in “During the summer I like to travel.” However, such omission is arbitrary when such sentences are compared to those with longer introductory phrases — and wrong in the case of transitional tags like finally, furthermore, and unfortunately — and for the sake of consistency, a comma should follow any introductory word or phrase.
6. Short Independent Clauses
In brief sentences such as “I will sort and you can staple” that consist of two independent clauses (complete thoughts that could stand on their own as distinct sentences), writers often choose to omit the otherwise obligatory comma before the conjunction.
But just as in the case of short introductory phrases, there is the problem of where to draw the line. Does one establish a rule about how many words each clause must contain to dictate whether a comma is employed, or does one judge each sentence on its own? Let simplicity be your guide: Always include a comma.
7. Coordinate and Noncoordinate Adjectives
When two or more adjectives sequentially modify a noun, depending on their relationship, they may or may not be separated by commas. To test whether to insert or omit commas, replace them with and. For example, “She was wearing a bright, cheerful expression” can also be written “She was wearing a bright and cheerful expression.” (The adjectives can be reversed in either case, too.)
However, “She was wearing a dark green blouse” cannot be rendered “She was wearing a dark and green blouse,” because dark and green describe the blouse in combination, whereas bright and cheerful separately describe the expression. Also, in this case, the adjectives cannot be reversed: “She was wearing a green dark blouse” is illogical because dark modifies green, not blouse. Therefore, no comma should separate the two terms.
Thanks for this excellent guide, Mark.
As a copy editor, I find people use them increasingly inconsistently, which often makes it difficult to be sure of the intended meaning.
You gave me a lot to think about. When considering whether or not to use a comma, I usually “listen” to the sentence, inserting a pause where I believe the comma should go. If it sounds right, I put in the comma. My rule of thumb is to make it easy and understandable to the reader so I avoid inserting a pause (comma) that will break the flow unless necessary to the meaning. You did not address Oxford commas, but I only use a comma before “and” when absolutely necessary for the meaning. I feel that “and” is linking words to keep the phrase flowing whereas a comma tells the reader to pause. I liken it to having a green light and a red light at the same time.
Wow, this can get so confusing. Could you also go into detail about when a comma should or should not precede the word “but”
Excellent advice. I have found that it can be difficult for a writer to proofread his or her text. I think writers subconsciously parse their own text which they know intimately and therefore don’t readily spot where punctuation is required for clarity of meaning. So, if you are trying to proofread your own text, I would suggest you leave some time between the writing and the proofreading.
Regards
Hi,
Comma before “because” is an interesting point that is mentioned here. Is this rule applicable to all conjunctions or is it restricted to only “because”? Could you please provide few more example with other conjunctions.
Thanks,
Kiran
Nice post. But shouldn’t “She was wearing a dark green blouse” be “She was wearing a dark-green blouse”? In this example, “dark green” seems like as an individual color.
CONFUSED – NEED CLARIFICATION
Definitely a lot of food for thought here, and I agree on most counts, but I am not so sure I agree with :
#2 Before Because
A sentence such as “I didn’t want to go because I hadn’t enjoyed myself last time” implies that the writer is explaining that the lack of enjoyment isn’t a factor in reluctance to attend an event; the reason for the reluctance will presumably follow.
It seems that whether WITH or WITHOUT the comma, this sentence implies ‘lack of enjoyment’ WAS a factor, which is the opposite of what you said.
To express that the desire not to go WAS NOT CAUSED by a previous bad experience, should it not read this way?: “I didn’t want to go, NOT because I hadn’t enjoyed myself last time, but beCAUSE (of this.)”
#2 because – the convention is surely that when the main clause comes before the subordinate clause (as in your example), there is no comma. Conversely, when the subordinate clause comes first, we use a comma. Given that, I can’t think many people would infer that “the lack of enjoyment isn’t a factor in reluctance to attend an event”; exactly the opposite.
If this was in fact what the speaker meant, in spoken language we would use stress and intonation to make this clear, perhaps stressing ” I hadn’t enjoyed myself”. But in writing surely we need to do something else to make this meaning clearer: a cleft sentence for example – “It wasn’t because I hadn’t enjoyed myself last time that I didn’t want to go.” Or use Joan’s solution.
Yeah, number two didn’t make sense to me either. As a writing tutor, I often hear people say they put commas in where they think a pause would sound good. I think this method causes a lot of errors. Commas are certainly challenging to use consistently and effectively.
Another viewpoint on 2: As I read it, the first example implies that the previous lack of enjoyment is not what made me want to attend the event. If I were explaining reluctance to attend, then I might say (although I won’t claim this to be correct grammar) “I didn’t not want to go because I hadn’t enjoyed myself last time.”
I think I’m going into a comma coma.
I’m glad I’m not the only one confounded by #2 because example.
To those confused, number 2 is exactly right even if not explained well. The particular example is poor because the assumed logical connection is stronger than the grammar(especially, I’m afraid, for people with low grammatical awareness). We all assume that if you don’t enjoy yourself that you don’t want to go, so we cannot read failure to enjoy oneself as even being discussed as a hypothetical REASON to want to go, even if it is grammatically implied (which it is, without the comma) to be exactly that. It’s more confusing because while put forth as a hypothetical reason to want go, it is also stated that this hypothetical reason was not the actual reason for wanting to go. This however is different from saying it was actually the reason for not wanting to go, which is what the comma adds. This is why scientific writing requires so much more precise grammar. The reader cannot make assumptions about the meaning when new complex technical relationships are being described, and the meaning must be clear from the grammar alone.
Without the comma the sentence says that failure to enjoy myself last time was not the reason I wanted to go this time. I didn’t want to go because of x; I wanted to go because of y. I didn’t want to go because Tom invited me; I wanted to go because I wanted to see the show. I didn’t want to go because I had a good time last time; I wanted to go to get ice cream. I didn’t want to go because I had bad time last time (as if I would like having bad times); I wanted to go for the drinks.
An adverbial clause with a comma on the end of a sentence becomes more than just adverbial. It becomes whole-sentence modifying. Instead of modifying “go” it modifies not wanting to go and now provides not a rejected reason to go, but rather a reason to not want to go. This trailing sentence-modifying clause demarcated with a comma has nothing to do with “because” specifically. It just happens that the word “because” is capable of being used in such clauses in a way where the ambiguity is particularly nasty.
I agree with Dan about #2. It’s just a confusing example.
Consider: “I didn’t buy a car because I wanted to travel.” vs. “I didn’t buy a car, because I wanted to travel.”
The first suggests I bought a car for another reason, such as commuting or impressing the ladies. The second implies I chose travel over car ownership. Now, I have seen sources that say a comma should never precede “because,” but I think this guideline ignores an important distinction in meaning. The rule outlined here in #2 is valuable to avoid misinterpretation.
In #7, I believe that “dark” is an adverb that modifies “green”.