Em Rule (n.): British. A dash of one em length that is used to create a strong sense of digression, associated thought, or an aside to the theme of a sentence.
The em rule is used as a pair to indicate a strong break during a sentence. They are used in a similar parenthetical way to two commas, but signify a break that is more pronounced. As a point of style you should avoid using more than one set of em rules per sentence, and many publishers don’t like more than one pair per paragraph. Brackets (parentheses) are sometimes used instead of two em rules.
As with parenthetical commas, the text before the opening em rule and after the closing em rule must flow were the em rules and the text inside to be removed.
In the final paragraph of the introduction I wrote:
‘However, my experience is that this style is not the most common in British publishing—look at a newspaper and see for yourself—so I have mentioned other commonly used styles where it seemed helpful.’
Removing the em rules and the text inside gives:
‘However, my experience is that this style is not the most common in British publishing so I have mentioned other commonly used styles where it seemed helpful.’
A second and perhaps more common use for the em rule is to introduce a phrase or afterthought at the end of a sentence. Here the em rule is similar to a colon but the two are not interchangeable, as the em rule is less formal than a colon and typically signifies an aside or afterthought in much the same way as the paired use does. There’s one used this way at the end of the introduction:
‘… they allow for the enhanced conveyance of emotion and precision through the use of text—and that is what we strive to achieve …’.
Note that there are no spaces before or after the em rule.
Adding a space either side of an em rule changes its significance to that of indicating that a word is missing:
‘… they allow for the enhanced conveyance of — and precision through the use of text—and that is what we strive to achieve …’.
[Note that an ellipsis (…) is more commonly used when there is more than one word missing.]
Adding a space on only one side of an em rule, before or after, signifies that part of the word to which the em rule is attached is missing:
‘… they —ow for the enhanced —vey— of emo— and precision through the use of text—and that is what we strive to achieve …’.
There is a general preference to use em rules instead of ellipses for omissions where an omission is enforced rather than natural, for instance to avoid a swear word: ‘No bl— swearing!’
[Note that an en rule signifies a missing letter whereas an em rule means a missing word or missing letters (as in the example above).]
The colon followed by an em rule combination (:—) is not used in modern UK English.
Em rules also have a specific use in bibliographies. In Oxford’s style, a double em rule is used instead of repeating the name of an author or authors in a list of their works. Think of it as a ditto dash for authors.
Doolittle (Dr), Communicating with Canines (Freelancealot, 2009)——and Otto, ‘Canine–Human Interaction’, Chew and Rip Magazine xvii, (2010), 15–33
[Dear Reader, for some reason WordPress produces a space between two consecutive em rules in the Doolittle example above. There should not be a space between the two em rules.]
‘Spaced En Rule’ as an Em-Rule Rule
Most publications that I’ve worked on simply don’t use em rules. Instead they substitute an en rule with a space either side. A quick glance through some newspapers, magazines, and books reveals this ‘spaced en rule’ style is clearly the most common in current British publishing.
There is a loss, when using this style, of the use of an em rule (now an en rule) to signify a missing word as the ‘space-en rule-space’ construction now signifies an afterthought. In defence of this style, ellipses can be used to represent missing words so the loss is not that limiting. However, this would require the use of ellipses rather than em (now spaced en) rules to represent missing letters as well, which stretches the limits of the stylistic use of ellipses – when (and yes, that’s a spaced en rule masquerading as an em rule) using the spaced-en style, should a closed ellipsis represent a missing letter and an open ellipsis represent one or more missing words? It’s a great example of how your choice of style in one area of grammar can have consequences in other areas.
One advantage of the spaced-en style to my eye is that, because of the spaces, the text is easier to read – and that’s an important advantage (as well as another example of a spaced en rule behaving as an em rule).
Another style is to not use en or em rules at all. Instead the writer, sub, or copy-editor substitutes alternative punctuation or recasts the sentence to avoid the necessity of the dash.
How to Produce Em Rules
The default shortcut on many Windows desktops is Ctrl+Alt+minus. On a Mac it’s Alt+Shift+hyphen.
[On my laptop the default is the same, but I had to turn the number lock on first.]
Three consecutive hyphens (—) can be used to represent an em rule should you be unable to create one.
Either use the shortcut (as above) or, with your cursor where you want the em rule to appear, click ‘Insert’ then select ‘Symbol…’. In the window that appears click the ‘Special Characters’ tab. Find and select the em rule from the list and click the ‘Insert’ button.
Word can create em rules from typed hyphens. Try typing a word followed by two hyphens and another word. [Note you should not add spaces around the two hyphens or you will get an en rule.]
The Concise Oxford English Dictionary states that an em rule—also known as a long dash or em dash—is ‘roughly the width of the letter M’. Oxford’s New Hart’s Rules is more precise: ‘An em is a unit for measuring the width of printed matter, equal to the height [not width] of the type size being used.’ So the length in millimetres of an em rule, being one em, depends on the size of font used: a 12pt font has an em rule of 12pt, which is 4.23mm (one-sixth of an inch). But we’ll leave the printers to haggle over any further refining of the definition of the length. Most folk will be using whatever length comes with their choice of word processor and font. Anyway, I’m reliably informed that it’s what you do with it that counts!
[As with all these grammar posts, your interesting and insightful comments are invited.]
Further Reading: En Rule (aka Short Dash, En Dash)