The Dilemma: You’re writing an important memo/ term paper/mental_floss book, and you need a dash. But not just any dash.

People You Can Impress: almost no one, really

The Quick Trick: It’s almost always an em dash. No document can ever contain too many em dashes—in this book alone we use 173.

The Explanation:
Having learned to not dangle your participles or split your infinitives,* grammar offers bolder, deeper mysteries. Like, can you start a sentence with like? And what about starting (or finishing) a sentence with and? And also, what’s the difference between an en dash and an em dash? The answers to those questions: Sure; yeah; and well, read on.

An en dash (–) is bigger than a hyphen but shorter than an em dash (—). Th e names come from an obscure typographical measurement system, but the dashes have now taken on a life of their own in grammar. The em dash is the spork of English grammar: It ain’t particularly pretty, but you can use it for most anything. Em dashes can replace colons or sets of parentheses, or represent a sudden change in thought or tone.

But if the em dash is a spork, then the en dash is nothing less than a salad fork: We often forget what it looks like and when to use it. But here are the two basic uses of en dashes:

1. To show numerical ranges, signifying “up to and including”—of dates, ages, pages, etc. (Example: “I read pages 7–22 last night.”)

2. The storied “compound adjective hyphen,” an event so rare in the English language that proofreaders shiver with excitement whenever they come across it. Basically “pro-American” gets a regular hyphen because “American” is only one word, whereas “pro–Falkland Islands” gets an en dash because “Falkland Islands” is two words. So, too phrases like “Civil War–era.”

The Grammar Roundup

Colon vs. Semicolon: Semicolons connect two complete sentences; colons start lists, introduce quotations, and extract water from feces. Oh, wait. Different colon.
Slash vs. Backslash: The backslash was invented in 1960 and is used almost exclusively in computing; the forward slash was invented by the ancient Romans and is often used in place of a hyphen.

What the ‽
The newest punctuation mark, by far, is the interrobang, which has the kind of name you just want to keep repeating. An exclamation point superimposed on a question mark, the interrobang is for those questions that are also exclamations, like: “Arnold Schwarzenegger is pregnant‽” Invented by advertising executive Martin K. Speckter in 1962, the interrobang became a key on some typewriters and was featured in newspapers. But alas, its popularity waned. Today you have to scroll all the way down your font list to Wingdings 2 to find the interrobang on Windows-based computers.

*Both of which, you will no doubt note, we did in that very sentence.