I didn’t learn the difference between the hyphen (-) and the dash (–) until I was working as a professional copyeditor. This was after four years of majoring in English as an undergrad, not to mention a masters degree! So I’ll preface this by noting that an engineer who knows the difference between these two marks of punctuation is likely the exception, rather than the norm.
As an engineer at a company writing a memo or report, you have a couple options when you are unsure about whether a word or phrase or set of words needs a hyphen or a dash. You can:
- Look up the word (or phrase) in a dictionary
- Let the copyeditors at your company work it out
The distinction between these two punctuation marks is as much a visual thing as it is a grammatical thing. In fact, some people call the hyphen “the n-dash,” because it’s the length of the letter n, and the dash the “m-dash,” because it’s the length of the letter m.
To type a hyphen, hit the key with two lines on it–the one the zero (0) and the equal size (=) once: –
To type a dash, press that same key TWICE: —
Now you know the difference between how these two symbols look. Let’s move on to their meanings and usages.
The hyphen isn’t just shorter (remember, it’s the n-dash, as opposed to the m-dash); it does less in a sentence than a dash. It can hold up part of a word or phrase, like ex-husband or mid-1980s or sixty-seven or over-the-counter or X-ray.
What a hyphen cannot do–because it is not strong enough–is hold up part of a sentence. For that, you’re gonna need a dash. See how I used a set of dashes to create a parenthetical statement in that previous sentence? I set off a phrase with dash on either end of it. If I had used a hyphen to do that, it would look like this-two hyphens trying to rope off a clause-and that would confuse my reader. Now that you know the difference between hyphens and dashes, notice how the sentence I just wrote (the one directly before this one) looks like I’m creating brand-new compound words, this-two and clause-and, rather than neatly delineating one clause from another.
The nice thing about dashes, once you’ve distinguished them from hyphens, is that they can be quite all-purpose. You can experiment with them when a semicolon isn’t right, but you want something stronger than a comma. Notice when writers use dashes in their work. It’s a pretty forgiving piece of punctuation, and one I think you’ll find quite useful in your own writing.