When you’re writing by hand, a hyphen and a dash can look pretty similar, although the meanings differ. You might throw in a hyphen to link two well-known words or add a dash—for impact, of course.

If you’ve ever found yourself confused about the difference between a dash and a hyphen, and when to use a hyphen, you’re far from alone. When you handwrite them, they probably look exactly the same.

Just a few years ago, the em dash was an ordinary form of punctuation used by writers to emphasize, interrupt and set aside ideas. (It gets its name from typesetting, historically being the exact ...