Serial Comma :
Use a comma to separate the elements in a series (three or more things), including the last two. "He hit the ball, dropped the bat, and ran to first base." You may have learned that the comma before the "and" is unnecessary, which is fine if you're in control of things. However, there are situations in which, if you don't use this comma (especially when the list is complex or lengthy), these last two items in the list will try to glom together (like macaroni and cheese). Using a comma between all the items in a series, including the last two, avoids this problem. This last comma—the one between the word "and" and the preceding word—is often called the serial comma or the Oxford comma. In newspaper writing, incidentally, you will seldom find a serial comma, but that is not necessarily a sign that it should be omitted in academic prose.
Sometimes the appositive and the word it identifies are so closely related that the comma can be omitted, as in "His wife Eleanor suddenly decided to open her own business." We could argue that the name "Eleanor" is not essential to the meaning of the sentence (assuming he has only one wife), and that would suggest that we can put commas both before and after the name (and that would, indeed, be correct). But "his wife" and "Eleanor" are so close that we can regard the entire phrase as one unit and leave out the commas. With the phrase turned around, however, we have a more definite parenthetical element and the commas are necessary: "Eleanor, his wife, suddenly decided to open her own business." Consider, also, the difference between "College President Ira Rubenzahl voted to rescind the withdrawal policy" (in which we need the name "Ira Rubenzahl" or the sentence doesn't make sense) and "Ira Rubenzahl, the college president, voted to rescind the withdrawal policy" (in which the sentence makes sense without his title, the appositive, and we treat the appositive as a parenthetical element, with a pair of commas).
As pointed out above (Rule #3), an adverbial clause that begins a sentence is set off with a comma:
When an adverbial clause comes later on in the sentence, however, the writer must determine if the clause is essential to the meaning of the sentence or not. A "because clause" can be particularly troublesome in this regard. In most sentences, a "because clause" is essential to the meaning of the sentence, and it will not be set off with a comma:
Sometimes, though, the "because clause" must be set off with a comma to avoid misreading:
Without that comma, the sentence says that Nixon's resignation was the fault of my sister-in-law. Nixon did not resign because my sister-in-law worked in the White House, so we set off that clause to make the meaning clearly parenthetical.
When a parenthetical element — an interjection, adverbial modifier, or even an adverbial clause — follows a coordinating conjunction used to connect two independent clauses, we do not put a comma in front of the parenthetical element.
When both a city's name and that city's state or country's name are mentioned together, the state or country's name is treated as a parenthetical element.
When the state becomes a possessive form, this rule is no longer followed:
Also, when the state or country's name becomes part of a compound structure, the second comma is dropped:
An absolute phrase is always treated as a parenthetical element, as is an interjection. An addressed person's name is also always parenthetical. Be sure, however, that the name is that of someone actually being spoken to. A separate section on Vocatives, the various forms that a parenthetical element related to an addressed person's name can take, is also available.
Use a comma to separate coordinate adjectives. You could think of this as "That tall, distinguished, good looking fellow" rule (as opposed to "the little old lady"). If you can put an and or a but between the adjectives, a comma will probably belong there. For instance, you could say, "He is a tall and distinguished fellow" or "I live in a very old and run-down house." So you would write, "He is a tall, distinguished man" and "I live in a very old, run-down house." But you would probably not say, "She is a little and old lady," or "I live in a little and purple house," so commas would not appear between little and old or between little and purple.
And what does a comma do, a comma does nothing but make easy a thing that if you like it enough is easy enough without the comma. A long complicated sentence should force itself upon you, make you know yourself knowing it and the comma, well at the most a comma is a poor period that lets you stop and take a breath but if you want to take a breath you ought to know yourself that you want to take a breath. It is not like stopping altogether has something to do with going on, but taking a breath well you are always taking a breath and why emphasize one breath rather than another breath. Anyway that is the way I felt about it and I felt that about it very very strongly. And so I almost never used a comma. The longer, the more complicated the sentence the greater the number of the same kinds of words I had following one after another, the more the very more I had of them the more I felt the passionate need of their taking care of themselves by themselves and not helping them, and thereby enfeebling them by putting in a comma.
So that is the way I felt about punctuation in prose, in poetry it is a little different but more so ...
Use a comma to set off quoted elements. Because we don't use quoted material all the time, even when writing, this is probably the most difficult rule to remember in comma usage. It is a good idea to find a page from an article that uses several quotations, photocopy that page, and keep it in front of you as a model when you're writing. Generally, use a comma to separate quoted material from the rest of the sentence that explains or introduces the quotation:
If an attribution of a quoted element comes in the middle of the quotation, two commas will be required. But be careful not to create a comma splice in so doing.
Be careful not to use commas to set off quoted elements introduced by the word that or quoted elements that are embedded in a larger structure:
And, instead of a comma, use a colon to set off explanatory or introductory language from a quoted element that is either very formal or long (especially if it's longer than one sentence):
in fiction : "The purpose and strength of . . . . "
Use commas to set off phrases that express contrast.
(Some writers will leave out the comma that sets off a contrasting phrase beginning with but.)
Use a comma to avoid confusion. This is often a matter of consistently applying rule #3.
Grammar English's Famous Rule of Punctuation: Never use only one comma between a subject and its verb. "Believing completely and positively in oneself is essential for success." [Although readers might pause after the word "oneself," there is no reason to put a comma there.]
Typographical Reasons: Between a city and a state [Hartford, Connecticut], a date and the year [June 15, 1997], a name and a title when the title comes after the name [Bob Downey, Professor of English], in long numbers [5,456,783 and $14,682], etc. Although you will often see a comma between a name and suffix — Bob Downey, Jr., Richard Harrison, III — this comma is no longer regarded as necessary by most copy editors, and some individuals — such as Martin Luther King Jr. — never used a comma there at all.
Use Commas With Caution :
As you can see, there are many reasons for using commas, and we haven't listed them all. Yet the biggest problem that most students have with commas is their overuse. Some essays look as though the student loaded a shotgun with commas and blasted away. Remember, too, that a pause in reading is not always a reliable reason to use a comma. Try not to use a comma unless you can apply a specific rule from this page to do so.
Concentrating on the proper use of commas is not mere form for form's sake. Indeed, it causes writers to review their understanding of structure and to consider carefully how their sentences are crafted.
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