Today’s topic is dashes: when to use them and when not to use them. At the risk of boring you—although you are reading a post about dashes so you really have only yourself to blame—I am going to start with the distinction between hyphens and dashes. A hyphen joins two words into a unit (e.g., ‘on-site manager’ or ‘lotus-eater’) or indicates a word break at the end of a line of text. A short dash (often called an en-dash because it is the width of the letter ‘n’) separates items such as dates or page numbers (e.g., 1711–1776 or pp. 106–7). A long dash (often called an em-dash because it is the width of a letter ‘m’) is what we will be talking about below. A hyphen is produced by a simple keystroke on your keyboard; dashes are symbols that can be inserted into a document in a variety of ways. For more on hyphens and dashes, you can consult the online Chicago Manual of Style.
Just in case anyone is still reading, I am now going to talk about using dashes in your writing. First, we will look at single dashes, which I will argue are insufficiently formal for academic writing, although some would disagree. Here is an example:
Recombinant DNA technology has left an indelible mark on the basic ingredient of human survival—food production.
This dash could be replaced by either a comma or a colon. I would suggest a colon because a colon signals unambiguously that what follows will complement or complete what precedes it. A comma would work, but since commas play so many roles in our writing, I generally choose a colon over a comma when they go head-to-head. Here is another example:
The range of Hume’s writings help us to understand his reservations about a revolutionary approach—such an approach would be unlikely for a thinker so immersed in historical considerations.
In this case, you could replace the dash with either a semicolon or a period. Generally, a semicolon will work best since it will provide the closeness that the author was trying to convey with the dash.
I am only arguing against the single dash in academic writing—it is absolutely fine in a more casual context like, say, a blog post. My reason for this advice is that the dash can play the role of a comma, colon, or period without doing anything unique. Nothing special is added and something may be lost. You may lose clarity, and you will certainly lose formality. I am being, of course, overly opinionated; if you wish to defend the use of single dashes in formal writing, I hope you’ll do so in the comments below. One possible line of defence is certainly the drama of the single dash; since it breaks up a sentence in an unconventional manner, it does draw real attention to what follows it. Now let’s turn to the use of double dashes.
Double dashes are used instead of commas (or parentheses) to interrupt a sentence. The phrase separated by dashes must be grammatically inessential, by which I simply mean that the sentence will still work without that phrase. Here is an example:
The issues that confront students entering late-stream French immersion programs—most importantly, their lack of familiarity with instructional vocabularies—are a pressing concern for school administrators.
It is often said that we use dashes to signal that something crucial is being added to a sentence and use parentheses to signal that the interruption is relatively unimportant (e.g., to give dates or citations or examples). In this schema, commas fall somewhere in the middle. There is some truth to this division, but I find the next three principles more helpful in deciding whether to use double dashes:
1. Most importantly, double dashes can be used to add an element to a sentence that already has its share of commas.
2. Double dashes are very common in some fields (most humanities fields, for instance) and rare in others (in many scientific fields, for instance). If they are rare in your field, it is unlikely that you would want to use them.
3. Regardless of field, double dashes are a stylistic variant and should be used sparingly; they draw attention to themselves, and the audience will grow tired of them if they are overused.
Overall, I suggest using double dashes—if they are appropriate to your field of study—in moderation and replacing single dashes with colons, commas, or even periods, if only in your formal writing.
Note: For more on dashes, see Interrupting Yourself.
Explorations of Style 
As boring as it may sound I really enjoyed this post. I have been reading quite a bit about dashes and when to use them this week (boring I know) and this post has solidified all the information to one manageable post. I’ve ‘starred’ this post in my Google Reader for further reference. Thanks.
Thanks, Jonny. I enjoyed looking through your blog! Good luck with your dissertation.
Thanks. I love your blog – it’s been added to my google reader.
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I disagree with your argument that dashes are unacceptable for formal writing. William Strunk, a grammarian, states, ” A Dash is a mark of separation, stronger than a comma…”(Strunk, 1999). I was taught to use dashes while in English 101, 102, and while in literature classes. I was challenged, however, on the use of dashes by the instructor – when presenting my Capstone Final. Nonetheless, there is no evidence to suggest that the use of dashes makes a sentence less reader-friendly, nor is there evidence to truly identify what makes writing formal or informal – as it is understood to be taken one way or another, by the reader.
Nonetheless, I enjoyed reading your blog; best wishes!
Reference:
Strunk, William. (1999). The Elements of Style, Fourth Edition. Longmann Publishing Company. ISBN-13: 978-0205309023
Christopher Bowden
Thanks for your comment, Christopher. I agree that formality exists in the eyes of the reader rather that in an easily identifiable set of rules. The attempt to create a sufficiently formal style is an attempt on the part of the writer to anticipate what will strike the reader as appropriate in the context. One reason that writing can seem informal is a lack of precision; this imprecision can be the result of many different features, including the single dash. The single dash can be replaced by a comma, a colon, or a semicolon, each of which gives the reader more precise information about the relationship between what comes before and after. As I’ve said often on this blog, the double dash is completely different. It is sufficiently formal because its meaning is entirely clear: the writer is interrupting the sentence. Overuse of this technique–something of which I am entirely guilty–can be annoying to the reader, but it is not inherently informal.
I don’t ultimately think that formality is a crucial issue for an experienced academic writer. Most writers find the tone that works for them and may or may not choose to include various elements that are, by some measure, less formal. But novice academic writers may find it helpful to think about the relationship between formality and precision in their writing.
enjoyable as well as practical. Thanks