One of the most common mistakes I come across is when commas are added where they shouldn’t be or left out where they’re needed. Incorrect commas is a big problem especially as it concerns quotes, dialogue, and parenthesis, so hopefully today’s grammar tip will help clarify the confusion.
|| Commas with Quotes
Quoted material is usually introduced with a comma. However, there are cases where inserting a comma before a quotation is not correct, such as when the quotation is preceded by that, whether, or a similar conjunction. [See: CMOS 16th ed. 6.50]
I believe it was President Kennedy who said, “Ask not what your country can do for you, ask what you can do for your country.”
BUT, consider: Franklin D. Roosevelt said that December 7, 1941, was a day that “would live in infamy.”
Both examples are correct, yet one used a comma and one did not. The difference is that in the second example, there’s the word that to introduce the quote, which essentially takes the place of the comma.
|| Commas with Dialogue
When considering spoken dialogue, such as that between two characters in a book, use a comma to connect the dialogue with the dialogue tag. However, when there is no dialogue tag and only an action tag, a period is used instead of a comma. (See this post for more on dialogue tags)
“I love apples,” she said.
“I love them too.” He took a large bite from the apple he was holding. “Especially the red ones.”
Both examples are correct, but in the second example, there is a complete sentence after the dialogue, so you need a period to close off the dialogue from the next phrase. In the first example, a comma is correct, because the dialogue tag and dialogue itself are connected.
|| Commas with Parenthesis
This is where I see the most confusion. People always want to put commas before a parenthesis, but this is never correct. [See: CMOS 6.53]
(From CMOS) After several drummers had tried out for the part (the last having destroyed the kit), the band decided that a drum machine was their steadiest option.
(From CMOS) Her delivery, especially when she would turn to address the audience (almost as if to spot a long-lost friend), was universally praised.
In both cases the comma comes after the closing parenthesis. This is incorrect: After several drummers had tried out for the part, (the last having destroyed the kit) the band decided that a drum machine was their steadiest option.
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Hopefully this gives you a basic idea of comma rules regarding these three situations! Let me know in the comments if you have any questions.