From: msb@sq.sq.com (Mark Brader)
Subject: What is a dash?  (Was "have went" & Re: This usage, it...)
Organization: SoftQuad Inc., Toronto, Canada
Date: Fri, 4 Sep 92 08:04:13 GMT

[Side note: when posting an article responding to a single subsidiary
 item in another article, remember to change the Subject line.  I've
 done it now, but that's one article too late in the thread.]

> > Yet another thing to make one wince is the ASCII pseudo-typography,
> > which makes dashes look like hyphens (or pairs thereof) and hyphens
> > look like minus signs.
> 
> So what's the difference between a dash and a hyphen?  Serious question
> here, not meant to be sarcastic at all.

There are actually four similar-looking characters, all of which are
distinguished in proper typography:  minus sign, hyphen, en dash, and
em dash.  En and em are typographers' measures; basically, an em is a
width equal to the height of the type, and an en is half that.  But
here they're just being used as names, like the way a Quarter Pounder
actually weighs something like 3.2 ounces.

The hyphen may be thought of as a "word-level" punctuation mark; it
ties two words into a compound word, either a nonce formation or a
standard one like "long-lived".  (I note in passing that such form-
ations tend to progress from two-word phrases to hyphenated forms to
single words, and that they seem to hover longer in the intermediate
hyphenated form in Britain than in North America.)  A hyphen also ties
together the halves of a word split between lines, like "formations"
in the previous sentence.  And it can indicate a partial word, as in
"both super- and ordinary highways were built" or "the suffix '-tion'".
All the "-" marks in this message up to this point are hyphens.

In typeset text, the hyphen is the shortest of the four punctuation marks,
often about the width of a lower case "t"; it is often made relatively
fat, for visibility, and never has space on either side of it except
when at the end of a line or when indicating a partial word.

The simple "-" character in ASCII or typewriter character sets is
primarily a hyphen, and "-" is used to represent a hyphen in both TeX
and troff input.

The em dash, or simply dash, operates at the phrase or sentence level.
It can be used in pairs--like this--with much the same meaning as
parentheses.  The second dash of such a pair is omitted if it would come
at the end of the sentence--like this.  It can also be used something
like a colon or semicolon between two related sentences--this is an
example of that.  It can be used at the end of an incomplete sentence,
especially in speech, like an ellipsis; whereas the ellipsis suggests
trailing off, the dash suggests breaking off, like--  Oh, I forgot to
mention that ellipsis means "...".   --And there is a similar, rarer
use at the beginning of a sentence.

The (em) dash is the widest of the four characters in typesetting,
as wide as a wide capital letter like W or even more.  To avoid an
excessive visual impact it is usually a very thin line.  The most
common style is to typeset it without spaces around it, except at
the end of a broken sentence, but some prefer to always use spaces.
There is also a style where an en dash (see below) is used with spaces
around it in place of an em dash.

In ASCII or typewriter text, the dash is usually represented by "--",
with or without spaces around it.  In TeX input it is "---" (which is
also seen occasionally on Usenet), and in troff input, "\(em".

The en dash is a more specialized character, used principally in range
constructs like "pages 5-7" (meaning pages 5, 6, and 7) or "page 5-7"
(meaning page 7 of chapter 5).  In these uses it does not have any
spaces around it, except when expressing an open-ended range as in
"Mark Brader (1955- )".  In ASCII or typewriter text, a simple hyphen
is used, while TeX input uses "--".  Troff does not officially have
this character, but "\-" is used for it sometimes in practice.

The minus sign, of course, is used in numerical expressions.  Typograph-
ically it may resemble an en dash or em dash, but it is placed higher,
to be centered on the height of a numeral (at least when full-height
"lining" numerals are used rather than the "old-style" numerals where the
number "6109" looks something like "biog").  In ASCII or typewriter text
it is written as a hyphen; in TeX input, a hyphen in math mode is used;
and in troff input, "\(mi" (which may be obtained from "-" using eqn).

All this is from memory, and I may have forgotten some specialized
usages of the different characters.
-- 
Mark Brader		"'"'Tisn't very easy to tell if a '"' or ''' mark
utzoo!sq!msb		is an opening or closing quote or ditto or prime,"
msb@sq.com		said Mark,' said 6'2" d'Artagnan," said Mark Brader.

This article is in the public domain.