A comma usually separates a direct quotation from a phrase identifying its source or speaker. If the quotation is a question or an exclamation and the identifying phrase follows the quotation, the
comma is replaced by a question mark or an exclamation point.

• She answered, "I'm afraid it's all we've got."
• "The comedy is over," he muttered.
• "How about another round?" Elaine piped up.
• "I suspect," said Mrs. Horowitz, "we haven't seen the last of her."
• "You can sink the lousy thing for all I care!" Trumbull shouted back.
• "And yet . . . [,]" she mused.
• "We can't get the door op—" Captain Hunt is heard shouting before the tape goes dead.

In some cases, a colon can replace a comma preceding a quotation.

When short or fragmentary quotations are used in a sentence that is not primarily dialogue, they are usually not set off by commas.

• He glad-handed his way through the small crowd with a "Looking good, Joe" or "How's the wife" for every beaming face.
  
• Just because he said he was "about to leave this minute" doesn't mean he actually left.
  

Sentences that fall within sentences and do not constitute actual dialogue are not usually set off with commas. These may be mottoes or maxims, unspoken or imaginary dialogue, or sentences referred to as sentences; and they may or may not be enclosed in quotation marks. Where quotation marks are not used, a comma is often inserted to mark the beginning of the shorter sentence clearly.

"The computer is down" was the response she dreaded.

• He spoke with a candor that seemed to insist, This actually happened to me and in just this way.
• The first rule is, When in doubt, spell it out.

When the shorter sentence functions as an appositive (the equivalent to an adjacent noun), it is set off with commas when nonrestrictive and not when restrictive.

• We had the association's motto, "We make waves," printed on our T-shirts.
• He was fond of the slogan "Every man a king, but no man wears a crown."

A comma introduces a directly stated question, regardless of whether it is enclosed in quotation marks or if its first word is capitalized. It also introduces a tag question.

• I wondered, what is going on here?
  
• The question is, How do we get out of this situation?
  
• That's obvious, isn't it?

A comma is not used to set off indirect discourse or indirect questions introduced by a conjunction (such as that or what).

• Margot replied quietly that she'd never been happier.
  
• I wondered what was going on here.
  
• The question is how do we get out of this situation.

The comma is usually omitted before quotations that are very short exclamations or representations of sounds.

• He jumped up suddenly and cried "I've got it!"

A comma may indicate the omission of a word or phrase in parallel constructions where the omitted word or phrase appears earlier in the sentence. In short sentences, the comma is usually omitted.

• The larger towns were peopled primarily by shopkeepers, artisans, and traders; the small villages, by peasant farmers.
  
• Seven voted for the proposal, three against.
  
• He critiqued my presentation and I his.

A comma sometimes replaces the conjunction that.

• The smoke was so thick, they were forced to crawl.
  
• Chances are, there are still some tickets left.