comma (,)
(Slightly modified) snippets from Associated Press Stylebook 2002, typed up for my easy reference.
IN A SERIES:
Use a comma before the concluding conjunction in a complex series of phrases: The main points to consider are whether the athletes are skillful enough to compete, whether they have the stamina to endure the training, and whether they have the proper mental attitude.
Use a dash or semicolon for cases when elements of a series contain internal commas.
WITH EQUAL ADJECTIVES:
Use commas to seaparate a series of adjectives equal in rank. If the commas could be replaced by the word and without changing the sense the adhectives are equal: a thoughtful, precise manner; a dark, dangerous street.
WITH NONESSENTIAL CLAUSES:
A nonessential clause must be set off by commas. An essential clause must not be set off from the rest of a sentence by commas.
WITH NONESSENTIAL PHRASES:
A nonessential phrase must be set off by commas. An essential phrase must not be set off from the rest of a sentence by commas.
WITH INTRODUCTORY CLAUSES AND PHRASES:
A comma is used to separate an introductory clause or phrase from the main clause: When he had tired of the mad pace of New York, he moved to Dubuque.
The comma may be omitted after short introductory phrases if no ambiguity would result: During the night he heard many noises.
But use the comma if its omission would slow comprehension: On the street below, the curious gathered.
WITH CONJUNCTIONS:
As a rule of thumb, use a comma if the subject of each clause is expressly stated: We visited Washington, and our senator greeted us personally. But no comma when the subject of the two clauses is the same and is not repeated in the second: we are visiting Washington and plan to see the White House.
The comma may be dropped if two clauses with expressly stated subjects are short. In general, however, favor use of a comma unless a particular literary effect is desired or if it would distort the sense of a sentence.
BEFORE ATRIBUTION:
Use a comma instead of a period at the end of a quote that is followed by attribution: "Rub my shoulders," Miss Cawley suggested.
Do not use a comma, however, if the quoted statement ends with a question mark or exclamation point: "Why should I?" he asked.
WITH YES AND NO:
Yes, I will be there.
IN DIRECT ADDRESS:
Mother, I will be home late. No, sir, I did not take it.
IN A SERIES:
Use a comma before the concluding conjunction in a complex series of phrases: The main points to consider are whether the athletes are skillful enough to compete, whether they have the stamina to endure the training, and whether they have the proper mental attitude.
Use a dash or semicolon for cases when elements of a series contain internal commas.
WITH EQUAL ADJECTIVES:
Use commas to seaparate a series of adjectives equal in rank. If the commas could be replaced by the word and without changing the sense the adhectives are equal: a thoughtful, precise manner; a dark, dangerous street.
WITH NONESSENTIAL CLAUSES:
A nonessential clause must be set off by commas. An essential clause must not be set off from the rest of a sentence by commas.
WITH NONESSENTIAL PHRASES:
A nonessential phrase must be set off by commas. An essential phrase must not be set off from the rest of a sentence by commas.
WITH INTRODUCTORY CLAUSES AND PHRASES:
A comma is used to separate an introductory clause or phrase from the main clause: When he had tired of the mad pace of New York, he moved to Dubuque.
The comma may be omitted after short introductory phrases if no ambiguity would result: During the night he heard many noises.
But use the comma if its omission would slow comprehension: On the street below, the curious gathered.
WITH CONJUNCTIONS:
As a rule of thumb, use a comma if the subject of each clause is expressly stated: We visited Washington, and our senator greeted us personally. But no comma when the subject of the two clauses is the same and is not repeated in the second: we are visiting Washington and plan to see the White House.
The comma may be dropped if two clauses with expressly stated subjects are short. In general, however, favor use of a comma unless a particular literary effect is desired or if it would distort the sense of a sentence.
BEFORE ATRIBUTION:
Use a comma instead of a period at the end of a quote that is followed by attribution: "Rub my shoulders," Miss Cawley suggested.
Do not use a comma, however, if the quoted statement ends with a question mark or exclamation point: "Why should I?" he asked.
WITH YES AND NO:
Yes, I will be there.
IN DIRECT ADDRESS:
Mother, I will be home late. No, sir, I did not take it.