USAGE

Among the multiple types of dashes (yes, there are many!), the most common ones are:

1. en dash, used:

• to indicate a list;
• to indicate a closed range (as a substitute of words ‘to’ or ‘between’);
• (less common) to hide letters in a word;
• to connect words in compounds (in some languages)

2. em dash, used:

• to indicate lines in a dialogue;
• (less common) to hide entire words or part of one.

Both en and em dashes are also used to enclose a section of a sentence, just like a pair of parentheses, or to indicate a separation within a sentence like a colon or semicolon.

HISTORY

Before the adoption of any punctuation standard, markers of various forms were used by scribes to indicate pauses. Dashes of various lengths have been used for many kinds of roles through the centuries, and across countries. But for dash-like symbols, these evolutions left us with the en dash and em dash as principal successors.

DESIGN

Their length has been standardized during the metal type printing era (in Europe and North America), using the size of the font as a reference for their measurement as such:

• 1 em = the font size;
• length of em dash = 1 em (or sometimes the width of letter M of the font);
• length of en dash = 1/2 of 1 em (or sometimes the width of letter n of the font).

Both are placed at the optical middle height between the baseline and ascenders. In a typeface style with contrast, the thickness of the dashes has to be visually consistent with that of the thin parts.

TYPOGRAPHIC RULES

Generally, in American English, it is preferred to use the em dash without space; and in British English, the en dash with a space before and after.

NOT TO BE CONFUSED

The en dash is particularly often confused with the hyphen (U+2010), the mathematical sign minus − (U+2212), or the hyphen-minus - (U+002D).

In digital fonts, each of these glyphs has its own Unicode. They are designed and can be accessed individually. But on modern keyboards—inherited from typewriter keyboards which had to make compromises on the number of glyphs due to the limited space available—we are still (mistakenly and without always knowing) often typing the hyphen-minus instead of the hyphen or the en dash. Thankfully, most intelligent text processing apps automatically replace the hyphen-minus with the correct glyph depending on the context.