As part of our online proofreading services at ProofreadNow, we often correct dash length in documents. Most people use the shortest form of a dash, the hyphen, for everything-not realizing that there are actually three different dash lengths and that each has a specific usage (like the em dash in this sentence). The purpose of this post is to give you an overview of the hyphen, en dash, and em dash as well as when to use each one.
The lowly, shortest-length, hyphen is indeed overworked. Its primary purposes are actually to create compound words (as in shortest-length) or to break a word across lines (as is often seen in newspaper or magazine articles). It is not intended for use in date or number ranges, nor to add a long pause for emphasis in a sentence; however, it is frequently misused in this manner. For more information, see Sections 6.81 and 6.82 of the Chicago Manual of Style, 15th Edition.
En Dash (–)
The purpose of the medium–length en dash is primarily to indicate ranges (of numbers, dates, etc.). Some people also use it – surrounded by a space on either side – as an em dash. For more information, see Sections 6.83-6.86 of the Chicago Manual of Style, 15th Edition.
Examples: World War II was fought in Europe from 1939–1944. Tonight's special event will last from 7:00–9:00.
Em Dash (—)
The longest of the dashes—the em dash—is used most often to set off an amplifying or explanatory element in a sentence, or to separate a subject from a pronoun. Though other punctuation marks, such as commas, parentheses, semicolons, and colons, can serve the same purpose, the em dash is typically used when extra emphasis is desired. As noted in the discussion of en dashes above, some prefer to express an em dash as an en dash surrounded by one space on each side; either expression—as long as it is applied consistently throughout the document—is acceptable in the absence of a style guide that dictates how the em dash should be expressed. For more information, see Sections 6.87-6.94 of the Chicago Manual of Style, 15th Edition.