破折号Dash

Em dash

The em dash is perhaps the most versatile punctuation mark. Depending on the context, the em dash can take the place of commas, parentheses, or colons⁠—in each case to slightly different effect.

Notwithstanding its versatility, the em dash is best limited to two appearances per sentence. Otherwise, confusion rather than clarity is likely to result.

Do not mistake the em dash (—) for the slightly narrower en dash (–) or the even narrower hyphen (-).

1. Use Em Dashes to Set Off Parenthetical Information

Em dashes are often used to set off parenthetical information. Using em dashes instead of parentheses puts the focus on the information between the em dashes.

For this usage, make sure you use two em dashes. Use one before the parenthetical information and one after it. Putting spaces before and after an em dash is a matter of preference; just be consistent. Consider the examples below for reference:

• While I was shopping—wandering aimlessly up and down the aisles, actually—I ran into our old neighbor.
• An etymological dictionary is one of the few books—no, it’s the only book—you’ll ever need.
• There has recently been an increase—though opposed fiercely by many people—in alternative education practices.
• He was going to call off the project—or was he?—when the client increased the payment.
• Traveling—that is, traveling by public transit—can be a relaxing activity if you bring music and reading material along with you.

Note that when dashes are used in place of parentheses, surrounding punctuation should be omitted. Compare the following examples.

1. Upon discovering the errors (all 124 of them), the publisher immediately recalled the books.
2. Upon discovering the errors⁠—all 124 of them⁠—the publisher immediately recalled the books.

When used in place of parentheses at the end of a sentence, only a single dash is used.

1. After three weeks on set, the cast was fed up with his direction (or, rather, lack of direction).
2. After three weeks on set, the cast was fed up with his direction⁠—or, rather, lack of direction.

2. Use an Em Dash to Set Off Appositives that Contain Commas

An appositive is a small section of extra information that is inserted into a sentence for clarification. Commas are usually used to offset the appositive, but if the appositive contains one or more commas, adding additional commas would be confusing for the reader. When using an appositive that contains a comma, offset it with dashes, instead.

• Four of us—Mike, Amanda, Katy, and I—went to the conference last week.
• Mr. M. glanced surreptitiously at his watch—his gold, diamond-encrusted watch—and suggested the meeting might adjourn for the day.
• If you need something, call my assistant—Catherine, not Margaret—and she’ll help you.
• Materialism—always wanting something more, something different—is good for the economy but bad for the soul.
• The question words—who, what, when, where, why, and how—are used to retrieve information in English.

3.Use an Em Dash to Bring Focus to a List

When a sentence begins with an independent clause and ends with a list, you can use a colon between the clause and the list. When the list comes first, it’s better to use a dash to connect the list to the clause.

• Dishes, laundry, dusting—they’re all done now, and I need a rest.
• Crocodiles, alligators—they both look the same to me and they look equally dangerous!
• Chocolate, strawberry, vanilla—all ice cream tastes good, especially on a hot summer’s day.
• Do this, do that, go here, go there—there’s so much to do that I don’t actually get much accomplished during the day.

4. The em dash in place of a colon

The em dash can be used in place of a colon when you want to emphasize the conclusion of your sentence. The dash is less formal than the colon.

• After months of deliberation, the jurors reached a unanimous verdict⁠—guilty.
• Even though its crocodilian jaws are fragile and incapable of eating a large animal, the Gharial still evokes a powerful emotion—terror.

5. Use an Em Dash to Mark Sharp Turns in Thought

Em dashes can also signal an interruption or a sudden change in the direction a writer was heading with a particular sentence. This technique is best suited for creative or informal writing. If you use it in academic writing, you might look unsure of yourself. Consider the examples below:

• Mary, could you—no, Mikey, don’t touch the sharp knife!—Mary, could you please set the table?
• Dinner is at 6:30—not 6:29 or 6:31.
• Where the heck is my—wait, what was I looking for?
• Would you please—oh, never mind.

更详尽Em dash使用说明

En dash

The en dash (–) is slightly wider than the hyphen (-) but narrower than the em dash (—). The typical computer keyboard lacks a dedicated key for the en dash, though most word processors provide a means for its insertion.

Span or range of numbers

The en dash is used to represent a span or range of numbers, dates, or time. There should be no space between the en dash and the adjacent material. Depending on the context, the en dash is read as “to” or “through.”

• The 2010⁠–⁠2011 season was our best yet.
• You will find this material in chapters 8⁠–⁠12.
• The professor holds office hours every Wednesday, 11:00 a.m.⁠–⁠1:00 p.m.

更详尽En dash使用说明