Hyphens, en-dashes, and em-dashes (and the bane of my existence)

There are three types of little hyphens (- – —) that may be used in English. This could be an interesting point to study for someone learning or writing English as a second language, as I have noticed that hyphens are used often differently in Spanish. In fact, I see this to be a perfect example of contextual habits and customs in written language. Another example of this is the differential use of quotation marks (“”) across languages.

This is a rather minor detail, as it is certainly more important to write with correct grammar and sentence structure. However, I frequently make corrections on hyphen and em-dash usage, and attending to this point is a simple way to improve one’s writing.

So, once again, here are the three little hyphen-like lines that you can use in English:

Hyphen: –

En dash: –

Em dash: —

Now, you are going to have to look at these very closely to the see the difference and that these little suckers are, in fact, different lengths. The hyphen is the shortest, and the em-dash is the longest. And the en-dash is a nice compromise in between the two. The only purpose of these little lines is to make your life more complicated while writing in English (just kidding).

Sometimes I imagine that one day, long, long ago… three little old men were sitting around a table at the Oxford Academy of the Proper and Correct Usage of the English Language (this is actually I name that I just invented two seconds ago while writing this) and decided to make things more difficult for their peons (also known as students) by inventing a new way to make writing even more complicated. Nevermind that you would rather just use a hyphen for everything – now you have to decide whether to use a hyphen, en-dash, or em-dash. The length of this little tiny line seems to make all the difference in the world (not really).

I request that you don’t take me seriously all the time.

Interestingly enough, there IS an Academia Real Española, the “official” royal academy in charge of dictating what is right and wrong in written (and in theory, spoken) Spanish.  To my knowledge, there is no single “academy” that dictates English usage, at least equivalent to the Spanish academy. In fact, true to English style, lots of authors have published their own guidelines that have converted themselves into semi-official Bibles of the English language. I would be curious to know as to whether or not there is in fact an “official” and recognized guideline or academy for the English language in the United Kingdom or any other English-speaking country, but certainly, in the United States, no single institution is seen as the ultimate authority on the subject.

But, as convention dictates, I will now outline their modes of usage.

– – —- – — – – — – – —- – — – – —- – —- – — – – —- –

Hyphens are almost always used to separate words or to separate a prefix from a root word. A lot of this usage, in my opinion, is based on custom, as many words have prefixes yet don’t automatically need to be written with a hyphen. Thus, hyphens are used, in a sense, to stress and highlight prefixes and their significance.

For example: pre- and post- treatment, semi-automatic, and check-in

Pre- and post- treatment is an interesting example worth looking at. Another similar example is mid- and long- term. Again, I should repeat that hyphens (-) are sometimes optional. For example, you could say both semiautomatic (without a hyphen) and semi-automatic (with a hyphen), and both are considered conventionally correct (unless you are following a style guide that dictates hyphen usage). As usual, I would say the most important thing is consistency (always or never use a hyphen for the same word every time it is repeated in your writing).

However, if you want more specific guidelines, Stephen Wilbers has written an excellent guide on hyphenated words, found at the following link:


Here, he has a list of many commonly hyphenated words and provides more exact guidelines for knowing when to hyphenate. This really is an excellent list and explanation, and I could never even attempt to re-create something as similarly wonderful. So, I wholeheartedly recommend his guidelines!

Let’s return now to the example of pre- and post- treatment, and mid- and long- term. In this case, the hyphen becomes a useful way of shortening your writing. For example, you could also say “in the midterm and longterm,” but “mid- and long- term” is a more aesthetically pleasing way to talk and write. You could also write “mid- and longterm,” but I would have preference for the “mid- and long- term” format, since I consider this to be more correct and to definitively highlight the prefixes as such. This formatting is frequently used in scientific writing.

Check-in, my final example from above, takes on a special meaning when used as a hyphenated word (vs. check and in, which have different meanings and usages on their own). So this is another application, so to speak, of hyphenated words.

For use in academic of scientific writing, the most frequent use for the en-dash (–) will be dates, months, and number ranges. I frequently see people write ranges of numbers or dates with hyphens, for example: 15-20 pairs, January 20-30. I have to admit that I am a stickler on this point, as the en-dash should be used for these instances, for example, the time period of 2000–2005 or a temperature range of 15–20 °C. I am beginning to think that this could in fact be an aesthetic concern, as I do indeed think that 2000–2005 (en-dash) looks prettier than 2000-2005 (hyphen). I should note that in the font used for this blog, the difference between the hyphen and en-dash is not very evident, but they are in fact, different lengths. In other fonts and font sizes, the difference may become more evident.

And finally, use em-dashes (a little bit longer than the en-dash) for separating two distinct but related ideas or to represent natural breaks in speech patterns. These have applications in formal and academic writing, but like many things in life – they are best when used in moderation. I frequently use these in personal communication and e-mails, since they just seem to work with a “train of thought” style of writing. For example:

Please let me know what you think – I can make any changes to your document if necessary.

This follows a very natural speech pattern and train of thought.

In 2005 in Mexico, the majority of crops produced were corn – Panama followed the same pattern.

The above is another example more relevant to academic writing, although in many cases you could just separate the two phrases above (by putting a period after the first phrase) or find a simpler way of formatting these ideas. So yes, em-dashes can add variety and spice to your writing, but only when you don’t over-spice it.

One final rule: no more than ONE em-dash per sentence. Just like the semi-colon, if you use too many… your reader will just get annoyed with you! Too much of anything is never a good thing.

Published by Allison M.

Technical and Scientific Writer, Editor, and Translator

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: