There are five principal uses of the comma:
- to separate clauses ([a]-[d])
- to set off a parenthetical element ([e])
- to mark a series ([f]-[g])
- to introduce a quotation ([h])
- to compel a pause for the sake of clearness ([i])
[91a.] A comma is used between clauses joined by but, for, and, or any other coördinating conjunction.
- Right: The hour arrived, but Forbes did not appear. [The comma emphasizes the contrast.]
- Right: She was glad she had looked, for a man was approaching the house. [The comma prevents the combination looked for a man.]
- Right: He gave the money to Burke, and Reynolds received nothing. [The comma prevents confusion.]
Exception.—If the clauses are short and closely linked in thought, the comma may be omitted (She came and she was gone in a moment. McCoy talked and the rest of us listened.) If the clauses are long and complicated, a semicolon may be used (See [92b]).
[Note.]—No comma should follow the conjunction. Wrong: He was enthusiastic but, inexperienced. Wrong: They went before the committee but, not one of them would answer a question.
[b.] Do not use a comma between independent clauses which are not joined by a conjunction. Use a period or a semicolon. (This error, the "comma splice," betrays ignorance of what constitutes a unified sentence. See [18].)
- Wrong: The circus had just come to town, every one wanted to see it.
- Right: The circus had just come to town. Every one wanted to see it.
- Wrong: The story deals with the life of a youth, Don Juan, his mother desired to make an angel of him.
- Right: The story deals with the life of a youth, Don Juan. His mother desired to make an angel of him.
- Wrong: My courses required very hard study, did yours?
- Right: My courses required very hard study. Did yours? [Or] My courses required very hard study; did yours?
- Wrong: He will assist you without the slightest hesitation, indeed he will do so with alacrity.
- Right: He will assist you without the slightest hesitation. Indeed he will do so with alacrity. [Or] He will assist you without the slightest hesitation; indeed he will do so with alacrity.
Exception.—Short coördinate clauses which are not joined by conjunctions, but which are parallel in structure and leave a unified impression, may be joined by commas.
- Right: He sowed, he reaped, he repented.