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I often see lists written as follows (using em dashes to elaborate a list item):

  • Item 1—explanation for item 1
  • Item 2—explanation for item 2

Is this generally correct, or are colons preferable?

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I'm not sure how this question relates to English. It seems like a proofreading question. Please correct me if I'm wrong. –  Matt Эллен Sep 28 '11 at 9:59
    
It's a grammar question. Are these not permitted? –  Hypercube Oct 2 '11 at 3:59

1 Answer 1

up vote 2 down vote accepted

While I'm not a typography specialist, I propose this to think about:

A colon might be useful for mappings between items and some associated, but generally unrelated information:

  • Day 1: A song that makes me happy
  • Day 2: A song that makes me sad

(inspired by the 30-day song challenge on Facebook)

If you write something which really elaborates on the item itself, you might use an em dash instead of a colon:

  • T-Rex—a carnivore
  • Stegosaurus—a herbivore

Another way to put it: Dashes are OK in situations where parentheses would also be acceptable, as in my second example, and probably also in your original example. Colons are to be used if the real information is after the item, as in the song challenge example. Parentheses would not be acceptable there, so I would prefer colons over dashes.

These are just suggestions; other people may prefer it the other way around or simply use them interchangably.

Also note that there are various definition environments in LaTeX and a definition list (<dl> with <dt> definition title and <dd> definition body) in HTML, and for real definitions or elaborations longer than one line, I strongly prefer this format (with the definition titles in bold, which is unfortunately not the default in most browsers.) It is also easy to create appropriate definition styles in Word and OpenOffice.

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Hmmm, interesting. I'm not sure about this, though. Aren't colons (in normal test) typically used in place of "namely", while em dashes are used to link unrelated thoughts? –  Hypercube May 23 '11 at 1:03
    
Ultimately, typography follows speech and dashes indicate pauses, which are useful for helping the adressee sort information. Therefore, the difference between a comma and a dash is, in my opinion, mostly one of pause length. Otherwise, the namely comparison is not so bad, but strongly depends on context. I think that colons and (single) dashes can often replace each other. You could read the Wikipedia articles on dashes and colons to add to the confusion. I mostly wanted to praise the definition list without bullets, but with bold items and indented definitions/elaborations :) –  Felix Dombek May 23 '11 at 5:11
    
Ah, okay. Thanks. –  Hypercube May 24 '11 at 2:41
1  
@Hypercube: I just thought of another explanation ... dashes are OK in situations where parentheses were also acceptable, as in the dino example, and probably also in your original example. Colons are to be used if the real information is after the item, as in the song challenge example. Parentheses would not be acceptable there, so I would prefer colons over dashes. –  Felix Dombek Sep 27 '11 at 23:09
    
Yes, I think that makes sense. I've seen en dashes often used as well, and I think these can replace parentheses. –  Hypercube Oct 2 '11 at 3:58

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