Grammar Rule #6: Use em dashes to set off parenthetical elements.
A parenthetical element is a word, phrase, or sentence inserted into the primary sentence to add information. It is a digression whose interruption of the sentence is pointed out by additional punctuation. This punctuation can be commas, parentheses, or dashes.
So, how do you choose between them?
1. Use commas when the additional information is closely tied to the content of the rest of the sentence.
My brother, a paleontologist, collects fossils.
Use a pair of commas to set off the extra information, unless the information ends the sentence and a period replaces the second comma.
The man who collects fossils is my brother, a paleontologist.
2. Use parentheses to indicate the additional information is minimal or so-so in importance.
The babysitter (our neighbor down the street) arrived late.
Always use a pair of parentheses to set off the extra information. At the end of the sentence, the period goes outside the closing parenthesis.
I always use the same babysitter (our neighbor down the street).
3. Use dashes to give emphasis to the additional information.
My sister—who can do no wrong, you know—was always the first to correct me.
Use a pair of dashes to set off the extra information, unless the information ends the sentence and a period replaces the second dash.
Always first to correct me was my sister—she who can do no wrong, you know.
Do not use more than two dashes per sentence. Use parentheses for additional parenthetical information.
My sister—who can do no wrong, you know—was always the first to correct me (yep, I deserved it).
Grammar Rule #7: Use a question mark or exclamation point before a dash, but not a comma, colon, or semicolon.
I ate a whole box of chocolates—what was I thinking?—and got sick.
I ate a whole box of chocolates—wow, they were good!—and got sick.
A period in an abbreviation may be used before a dash.
My whole family—grandparents, parents, sibs, nieces, etc.—pitched in to help me.
Parentheses may be used inside a parenthetical element set off by dashes.
My little brother—ever the faithful tattle-tale (we hated each other for years)—was never my chosen companion.
Grammar Challenge: Your Turn! Replace the X with the punctuation you think best sets off the parenthetical elements:
1. Sam’s wife X abandoned as a toddler X craves love and attention.
2. Sam’s wife X she’s quite a looker X craves love and attention.
3. Sam’s wife X Miss Idaho in 1996 X craves love and attention.
4. When we drove to Florida X it took twenty hours X gas cost a little over a dollar.
5. When we drove to Florida X our annual summer destination X gas cost a little over a dollar.
6. When we drove to Florida X without stopping, mind you! X gas cost a little over a dollar.
(Answers are below.)
WHAT GRAMMAR OR PUNCTUATION TOPICS WOULD YOU LIKE ME TO ADDRESS? I'M HERE FOR YOU!
1. Commas, because of the close tie to the content of the primary sentence.
2. Dashes, because of the emphasis on her looks.
3. Parentheses, because being Miss Idaho in 1996 is minimally important
4. Parentheses, because taking twenty hours is minimally important.
5. Commas, because of the close tie to the content of the primary sentence. Parentheses would also be acceptable if the information is considered minimally important.
6. Dashes, because of the emphasis on not stopping.