You can tell there’s something wrong with me when I have a favorite punctuation mark. It’s the en dash, the bastard middle child between the hyphen and em dash, but it can provide oh-so-much clarity and eliminate oh-so-much ambiguity once you learn a couple simple rules for when it should replace the hyphen. The en dash has the HTML code –, the Unicode number 2013, and can be found, for example, in the Insert | Symbol | Special characters box in Microsoft Word. The Wikipedia article on the en dash, or “n dash” as it is sometimes written because it was originally supposed to be the width of a capital N (I guess “en” is the transcription of the word for the letter N), is very informative. I also wrote a tutorial on the proper uses of the en dash, based on the Wikipedia article and my experiences editing biomedical research manuscripts, on my Grammar page.
The en dash has multiple usages: to represent a range of numbers, to mean “and” or “to”, and to take the place of the hyphen when one side of the hyphen or the other (or both) contains a space or hyphen. This post is about the third use: When you would normally use a hyphen to create a compound adjective or some other compound term, but either side of the hyphenated phrase has multiple words or a hyphenated word, then the hyphen should be replaced with the en dash. A few simple examples of this replacement might make you think it’s no big deal and shouldn’t ever be bothered with:
Probably every time you have encountered those phrases and others like it, the hyphen was used instead, and it was clear enough. It wasn’t as precise as it could be, and we have a perfectly good punctuation mark to make those phrases as precise as possible, so if you’re going to use one almost-right punctuation mark, why not use the right one? It might not be the difference between the lightning bug and the lightning, but as the examples below show, there are times when the difference between the hyphen and en dash is almost that big, so it is better to follow the rule uniformly than to follow it sometimes and ignore it others (just like the Oxford comma!).
The main purpose of this post is to provide some example phrases in which the hyphen is completely unacceptable and the en dash is the only suitable punctuation mark:
non-current smokers vs. non–current smokers
This example is taken from a paper in which the authors divided their study population into two groups: those who were current smokers and those who were not. Therefore, their two groups were current smokers and non–current smokers. The only possible way to express this in a concise way and using the terminology that the authors wanted was to use the en dash. The hyphen isn’t just unclear; it is categorically incorrect. Non-current smokers with a hyphen means people who were smokers but aren’t currently, i.e., past smokers (or I guess future smokers too), which would specifically exclude never-smokers, which would have been incorrect according to the analysis these authors performed. Many similar examples can be imagined in which the “future” possibility really does apply, such as a prospective study that was conducted on people who weren’t smokers but became smokers later in the study, or weren’t diabetics but became diabetics, or weren’t pet owners but became pet owners, etc. Non-current with a hyphen is an adjective that applies to smokers, whereas non–current smokers is a single noun identifying a different, more inclusive group: people who no longer smoke and people who never smoked.
conventional extract–treated group
This group wasn’t an extract-treated group that received some other conventional treatment that earned them the “conventional” label; they were treated with the conventional extract (of green tea or something or other), which can only be expressed with the en dash and not with the hyphen.
FGF stimulation–dependent SHP2 activation
With a hyphen, this phrase would mean FGF activation of SHP2 that is stimulation-dependent. Dependent on what stimulation? It makes no sense. It is SHP2 activation that is FGF stimulation–dependent. The need for the en dash in this phrase does come partly from the stilted, super-formal conventions of scientific writing. This phrase appeared at the end of a sentence that could have been written, under different circumstances with a different meaning, as “…FGF’s SHP2 activation” (“FGF’s activation of SHP2”), but apostrophes are way too frowned upon in primary literature, so the awkward phrase “the FGF SHP2 activation” could be totally legitimate, if the FGF protein directly activated the SHP2 protein. It does not. Stimulation with FGF leads to activation of the intracellular protein SHP2, so with the multiple-word antecedent, the en dash is necessary.
postprandial TRL–mediated foam cell formation
Again, this is not TRL-mediated foam cell formation that is postprandial; it is foam cell formation that is mediated by postprandial TRL.
small RNA–dependent scaffold
This is an especially good example because “small” is a common adjective itself. This phrase means a scaffold that depends upon small RNAs as a necessary component, in contrast to a small scaffold that requires RNAs.
inter–stress fiber space
This is another good example of a prefix (“inter”) that needs to be followed by an en dash instead of a hyphen in this phrase. This means the space in between stress fibers, not an “inter-stress” fiber space, whatever that would mean.
All of my examples are from biomedical research papers because that’s the writing I encounter the most. What are some good examples that you’ve come across of the need to replace hyphens with en dashes?