Hyphens and Dashes
Hyphens and dashes look like similar pieces of punctuation and are often created using the same keys on your keyboard, but they have different uses and functions.
A hyphen (-) is a piece of punctuation used to connect separate words or word parts that are intended to function as one.
The fifty–five–year–old athlete was just as qualified for the marathon as his younger opponents.
My doctor recommended against taking the medication, since it can be habit–forming.
A high-school student told me that.
My mother-in-law is coming to town this weekend.
A student in high school told me that it was a nerve-racking experience.
Word parts that are single letter also use hyphens, as seen in the examples below:
Is it correct to write e-mail as email (without the hyphen)? No, this is not yet fully accepted as correct in formal writing, but it is common in casual writing, and the momentum of change appears to be in favor of email, so it will likely be considered formally correct in the near future. This is one example of the continuous dynamic of change in English, and in language in general. Conscious efforts, expert judgments, cultural norms, historical events, and most of all common usage—these factors all play off of each other to change the language, or to keep it the same, over time.
Dash, or Em-dash
A dash (—), more technically known as an em-dash, is a punctuation mark used to set off abrupt interruptions in a sentence. You can enclose text between two em-dashes, or use just one em-dash. To create an em-dash in many word processing programs, type two hyphens together (without space in between). It is typically acceptable to leave two hyphens together to indicate an em-dash, but it is not correct to use just a single hyphen as an em-dash.
I arrived to the interview at noon—just in time to embarrass myself.
Any of the suits—except for the purple one—should be fine to wear.
The em-dash has very few concrete rules associated with it, so you can use it in all sorts of scenarios rather freely without fear of making grammatical mistakes. For instance, em-dashes can even be used to combine two independent clauses:
“That can’t be,” and “that’s inside the room” are both independent clauses that would normally require a semicolon, colon, or comma plus a coordinating conjunction, but the second clause acts abruptly enough here to use an em-dash, so this is correct.
So the em-dash gives you great punctuation power, but remember what comes with great power. Avoid going full Emily-Dickinson on your essays.