In our previous two columns, we explored the hyphen and the en dash. Now, we come to the largest of the dashed punctuation marks: the em dash (also sometimes just called a "dash").' Just as the en dash ( - ) gets its name from the fact that it's about the width of a capital letter N, the em dash's ( - ) name comes from the fact that it's as wide as a capital M.' The em dash has two primary uses: (1) to provide additional information in the middle of a sentence and (2) to change course or emphasize informa- tion at the end of the sentence. In this column, we'll cover the first use. Next time, we'll focus on the second use. A pair of em dashes can provide additional information in the middle of a sentence, just like a set of commas or parentheses.'