This question already has an answer here:

I'm wondering why there are three different sizes (perhaps more?) for lines that separate characters? I understand the grammatical usage (or rather, I could look it up), but the benefit to readers is not clear to me.

marked as duplicate by Jim, Nicole, Edwin Ashworth, Ellie Kesselman, ScotM Mar 10 '15 at 0:37

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 2
    You should ask @tchrist. – Robusto Mar 9 '15 at 17:01
  • 1
  • 1
    I think OP's question is not, "what are each of them for", but why does it make a difference? I.e., if everyone used a hyphen for everything, what confusion would it cause? – Jim Mar 9 '15 at 17:23
  • 2
    We've been here before. Since the lengths of these things differ with fonts (and some people still do real writing), real benefits are dubious when you get beyond the short one and the long one. In addition, usage is recommended by style guides rather than mandated by the Academy. – Edwin Ashworth Mar 9 '15 at 17:26
  • 1
    I'm voting to close this question as off-topic because it's not about the English language specifically. – Jim Mar 9 '15 at 17:27
up vote 5 down vote accepted

hyphen "The short one"
Its diminutive size helps the reader to read the two words as a single word. Ideally, this would be visually invisible and the two words would be directly joined, but grammar rules don't agree.

en-dash "The mid-sized one"
The difference in appearance is important in order to signal to the reader that it should not be interpreted as a compound word.

em-dash "The long one"
The length of this dash is so significant that it causes a mental pause similar to a semi-colon.

If your reader can infer the meaning of the character from the context of the sentence, it is acceptable to simply use a hyphen in all of these cases. The acceptability here is strictly a reader-perception measure and not at all grammar-related. If you are writing a piece that requires strict adherence to a style guide, you should follow that.

On a personal note, I find that a trailing space is usually required when using a hyphen in place of an em-dash.

Fun side note: en-dash and em-dash are named after the glyphs to which their lengths should match. You can use this to help you remember which one is longer: an n is shorter than an m.

Not the answer you're looking for? Browse other questions tagged or ask your own question.