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COMMA

See also ADJECTIVES AND ADVERBS, PUNCTUATION OF.

Variations in punctuation affect the meaning and the tone of a sentence. Sense and common sense allow the writer and the editor some leeway, but an exception should not be allowed to become the rule.

The modern trend is to use fewer commas than many of us were taught in school.
1. MODIFIERS BEFORE A NOUN
  Commas: If two modifiers before a noun can easily trade positions, separate them with a comma: these pretty, colorful villages; these colorful, pretty villages. However, this comma may sometimes be omitted: a hot sunny morning.
  No commas: When the order of the modifiers before a noun is normally fixed, do not use a comma: these ugly little towns; the hard tropical rain.
  Two commas: When one of the modifiers explains, amplifies, or partly contradicts an earlier modifier, use commas: my samloh, or pedicab, operator; a pleasant, though not magnificent, view. Do not put a comma after the final modifier simply because it has a modifier itself: men of that dim, often frigid past.

2. APPOSITION
  Commas: A term in apposition to another is set off with commas: beiju, or bitter manioc, cakes; We saw a lively play, Julius Caesar. Here the second term gives additional (nonrestrictive) information.
  No commas: When the second element is essential to the meaning (restrictive), there are no commas: The play Julius Caesar is billed for tonight's entertainment.

3. FAMILY RELATIONSHIPS
  Commas: In expressions like "My wife, Ann, smiled," set off the personal name when the person is the only one that bears the relationship. Bob and his wife, Ann; but Bob and wife Ann.
  No commas: In such expressions as "My brother Bill came running," the omission of commas shows that there are two or more brothers, one of whom is Bill.

4. SERIES
  Commas before and: In a series of three or more items, use a comma before the and, or, or nor: pepper, millet, and rice.
  And/and: When a series contains an and that links the last item to the series, and the last item itself contains an and, put a comma before the and that belongs to the series: water, milk, and canned and bottled beer.
  Semicolon: It is often best to use semicolons instead of commas to set off the members of a series if one or more contain internal commas.

5. COMMAS BETWEEN INDEPENDENT CLAUSES (COMPOUND SENTENCES)
  Commas: Use a comma between independent clauses joined by and, but, for, or, nor, either . . . or, neither . . . nor, so, yet, unless the clauses are short and closely joined in thought: The ice thins out and patches appear.
  Semicolon: When independent clauses are not connected by a conjunction, separate them with a semicolon (or a period): We looked all around; we liked what we saw. If the clauses are very short and simple, and quite closely linked in thought, commas may be used: I came, I saw, I conquered.

6. COMPLEX SENTENCES
  No commas: Two short dependent clauses joined by and, but, or, or nor are not separated by a comma: When the sun went down and the crickets called ...

    If the second independent clause in a sentence is preceded by a clause or phrase that should be set off by commas, no comma is necessary between that clause or phrase and the conjunction: At first he walked at a brisk pace, but when he got halfway up the hill, he slowed down.

7. RESTRICTIVE AND NONRESTRICTIVE CLAUSES AND PHRASES
  Commas: Clauses and phrases that are not essential to the meaning of the sentence (nonrestrictive) are set off by commas: Bernard G. Quarrick, who hails from Uniontown, follows the fortunes of the Penn State Nittany Lions. Bernard G. Quarrick, age 45, follows the fortunes of the Penn State Nittany Lions. The game started at two, when Bernie was still looking for a parking place.
  No commas: Clauses and phrases essential to the meaning of the sentence (restrictive) are not set off by commas: Bernie likes to eat peanuts while he's watching a game; the person who calls the tunes pays the piper; anyone over 14 may call the tunes; please let me know if you are interested in going.

8. COMPOUND PREDICATE
  Commas: If the "and" joining a compound predicate is preceded by a phrase also containing the conjunction "and," a comma may be used for readability between the two verbs: Turkey's largest city navigates economic and political shoals, and braces for the next big one.
  No commas: Unless some other guideline applies, do not put a comma between two verbs that have a common subject. In the two examples that follow, the first has a compound predicate (no comma), whereas the second has two independent clauses connected with and (comma): He came into the room with a bright smile and adjusted his tie. She came into the room with a bright smile, and the room seemed brighter too.

9. INTRODUCTORY CLAUSES AND PHRASES
Use a comma after a dependent clause that precedes the main clause of a sentence, after an introductory phrase that contains an infinitive or a gerund, and after a participle not used as an adjective before a noun:
    Since it was starting to rain, we left.
By burning their bridges, they. . . .
After the burning bridge came a succession of. . . .(burning used here as an adjective)
Being satisfied, they set to work.
Following the firemen, we came to. . . .
Following the hurricane some of the farmers. . . . (Following used here as a preposition; after would be clearer.)

  When the introductory matter contains no verb, its length and readability determine the need for a comma. Omit commas after short introductory phrases unless misreading could occur:
    By 1995 he was running the business by himself.
At the time, he was running the business by himself.
For the past 15 years U.S. utilities needed to add power.
Worldwide there has been an increase in zoonotic diseases.
Worldwide, people have the same basic needs.
With satisfied smiles they set to work.
My personal feeling is, we will have a concern in the next couple of decades.  

10. QUOTATIONS
A quotation of normal length (two sentences or less) is ordinarily set off by a comma. However, a very short quotation may not need one: The dog cried "Yap!"

A longer or more formal quotation is introduced by a colon.

A direct quotation that is not introduced by a verb of saying such as say, comment, shout, murmur, etc., is preceded by a colon. He pointed: "Look at the moon!"

A quotation preceded by a verb that has a direct object requires a colon. She murmured her reply: "Bring soft drinks next time."

11. DATES
Follow this style in punctuating dates:
    In January 1979 the. . .
On January 1, 1979, he. . .
Christmas Day, 1980, was. . .
Avoid: 6 January 1989

In the January 1979 issue
In spring 1979
the Fourth of July, 1776, was ...
12. CONJUNCTIVE ADVERBS
  Commas: Usage varies with conjunctive adverbs such as then, thus, besides, consequently, furthermore, hence, moreover, however, nevertheless, and therefore. Let meaning, intention, and rhythm be your guide. Then and thus generally need no commas to set them off: We see then that. . . . However and moreover generally take commas: The Navajo, however, preferred ...
  Semicolon: Put a semicolon between independent clauses that are linked only by a conjunctive adverb: We were late; therefore we hurried. If the clauses are extremely short, commas may be used for effect: We came, we saw, we conquered.

13. PAIRED COMMAS
Nonrestrictive material inserted within a clause requires a pair of commas, not just a single comma. A single comma cannot stand between a subject and its verb, a verb and its object, or a preposition and its object; use two commas or none.
    Incorrect: The profits, Werner insisted were not to be the sole purpose of the venture.
    Correct The profits, Werner insisted, were not from this stylebook.

14. COMMA WITH OTHER MARKS OF PUNCTUATION
  Quotation mark: A comma falls within the closing quotation mark: One term, "particular plantations," gave us trouble. For a quotation within a quotation, the comma falls within the single quotation mark.
  Parenthesis: When matter within parentheses is inserted where a comma belongs, the comma follows the second parenthesis: After the ball ended (we went home at five), the islanders. . . .
  Ellipsis: A comma that occurs in quoted matter is absorbed by the ellipsis mark (three dots). When an ellipsis ends a quotation, a comma may be added after the mark if required by the rules of punctuation: "Once upon a midnight dreary . . . ," he quoted darkly.
  Other punctuation A comma is absorbed by a colon, semicolon, dash, period, question mark, or exclamation point. A comma follows the trademark symbol or an asterisk.