5.6.4 En Rules and Em Rules

En rules. An en rule (sometimes called an ‘en dash’) is longer than a hyphen (see Section 5.2) and shorter than an em rule (see below); it can be used closed up without any spaces around it or with spaces on either side depending on its function. Although it has very specific uses, it often presents difficulties for authors, particularly because of confusion regarding whether an en rule or a hyphen should be used in a particular situation, and occasionally whether an en rule or em rule should be used. Some of the uses of en rules are noted in my discussions of numbers (in Section 6.4) and hyphenation (in Section 5.2), but the list I provide here is more comprehensive.

An en rule is used without spaces around it with the meaning ‘to’ or ‘and’ in the following situations:

• Between numerals that form a range, such as page numbers, dates and times (‘pp.22–54,’ ‘1995–2014’ and ‘9.30–10.45’), but it should not be used in combination with ‘between’ or ‘from’ (that is, ‘1995–2014,’ ‘from 1995 to 2014’ and ‘between 1995 and 2014’ are all correct, but ‘from 1995–2014’ and ‘between 1995–2014’ are not). When words are used instead of numerals, it is usually best to use a word instead of the en rule between the numbers as well.
• Between words that indicate a range, such as months and days of the week (‘January–April’ or ‘Monday–Saturday’) or locations on a route: ‘the London–York railway line’ or ‘the Tsawwassen–Swartz Bay ferry crossing.’ Here, too, the en rule should not be combined with ‘from’ and ‘between.’ Sometimes a slash (or solidus) will be used between such elements if either or both of them consist of more than one word: ‘the Tsawwassen/Swartz Bay ferry crossing’ (on the slash, see Section 5.6.5).

• Between elements of the date system used by the International Organization for Standardization: for example, ‘2014–11–04’ for ‘4 November 2014.’
• Between the elements of a ratio instead of the word ‘to’: ‘the flour–water ratio for dough,’ for instance, or ‘the chemotherapy–nonchemotherapy ratio of patients.’ A colon is sometimes used instead of the en rule in these cases, with or without a space on each side (the flour:water ratio).
• Between words or names to indicate a meeting place, such as ‘the Canada–United States border,’ or a competition or match, such as ‘the IceCaps–Marlies hockey game.’ Sometimes a slash is used instead of the en rule in such cases, especially if one or both of the elements consist of more than one word: ‘the Canada/United States border.’

• Between words to define a close relationship: ‘the author–editor relationship’ or ‘red–green colour blind.’ A slash is sometimes used instead of the en rule in these situations (red/green colour blind), especially if one or both of the elements consist of more than one word.
• Between words to indicate an alternative, as in ‘an on–off switch,’ though a slash is usually used in such situations (an on/off switch).
• Between the names of the coauthors of a theory or test, as in ‘the Mann–Whitney test’ or ‘the Taylor–Johnson theory,’ and in compound words or adjectives derived from two names, such as ‘Marxism–Leninism’ (noun) and ‘Marxist–Leninist’ (adjective).
• Between the names of people or nationalities to indicate a connection of some sort, such as ‘the Canadian–American negotiations’ or ‘a Chinese–Japanese heritage,’ but if the first part of the compound is a word that cannot stand on its own (a prefix, for instance), a hyphen should be used instead: ‘Sino-Japanese heritage.’
• After a prefix instead of a hyphen when the prefix is added to an open (unhyphenated) compound, such as ‘pre–Vietnam War,’ but this is more common in American than British English.

In many of the above situations, hyphens are often used instead of en rules, and some guidelines will even specify (via instructions or examples) that hyphens can or should be used (in page number ranges, for instance), so do check university or department guidelines to determine which is appropriate for your thesis. Keep in mind, however, that hyphens can cause confusion in some situations (see also Section 5.2). ‘Red-green’ with a hyphen, for instance, means a colour that is reddish green, not ‘red and green’ (as in ‘red–green colour blind’), and ‘author-editor’ with a hyphen means one person who is both an author and an editor, whereas with an en rule (author–editor) the term refers to two people – an author and an editor. Similarly, ‘Taylor-Jones’ with a hyphen indicates one person with a double name, whereas ‘Taylor–Jones’ with an en rule indicates two people, and the en rule retains this meaning even if one of the names is double barrelled (for example, ‘Olson–Kerby-Fulton’ refers to two people with the first named Olson and the second, Kerby-Fulton; were a hyphen used instead of the en rule, as in ‘Olson-Kerby-Fulton,’ the result would be confusing).

An en rule, in this case with a space before it, can be used to indicate that speech breaks off abruptly (Well, I never –), and en rules with spaces on both sides can also represent individual missing letters (Oh s – – t!). The most common function of spaced en rules, however, is to mark parenthetical clauses, in which case they indicate a more pronounced break in the sentence than commas would and highlight the parenthetical clause more than parentheses would (em rules can also be used for this purpose, as noted below; on commas and parentheses, see Section 5.6.1 and Section 5.6.5). If the clause appears in the middle of a sentence, en rules should be used to surround the clause: ‘I just saw a squirrel – a big grey one! – jumping from tree to tree across the canal.’

When the clause appears at the end of a sentence, the opening en rule functions rather like a colon (on which, see Section 5.6.1), though it is somewhat less formal and often expresses an aside or afterthought, and a closing en rule is not used: ‘I just saw a squirrel – a big grey one!’ No punctuation should precede an opening parenthetical en rule, and while the closing en rule of a parenthetical clause can be preceded by a question or exclamation mark (as I have in the example above), it should not be preceded by a comma, semicolon, colon or full stop. Although the use of en rules for parenthetical clauses is acceptable in formal prose, excessive use of en rules for parenthetical material (in every sentence, for instance) is poor style, and as a general rule no more than one parenthetical clause marked by en rules should be used in a single sentence.

Em rules. An em rule (also referred to as an ‘em dash’) is twice the length of an en rule, but has some similar functions. It is used, for instance, exactly as an en rule is to mark parenthetical clauses both within and at the end of sentences, especially in American English, but when it is used in this way, no spaces appear around it: ‘I just saw a squirrel—a big grey one!—jumping from tree to tree across the canal’ and ‘I just saw a squirrel—a big grey one!’ An em rule without a space before it can be used instead of an en rule to indicate that speech breaks off abruptly (Well, I never—); also without a space before it, an em rule indicates that part of a word is missing (They met secretly with Prince H—), and with spaces on both sides, it indicates that a whole word is missing (She claimed that — ran out the back door). Em rules are also used in bibliographies or reference lists to represent the name of an author (or the names of the authors) for second and subsequent items written by the same author(s), but this method should only be used if approved by your department and/or supervisor; generally speaking, author names should be repeated in full for each source or entry included in a list of references, and author names should always be given in full whenever the authorship changes in any way. Although an index is not usually required in a thesis, em rules can also be used to indicate repeated entry headings in an index.

PRS Tip: En rules and em rules are special characters in Word, and often problems and inconsistencies associated with the use of both kinds of dashes are caused because authors are unsure of how to produce these rules. Two methods are available by clicking on the Insert tab in the main menu of Word and then clicking on the Symbol button at the far right and on ‘More symbols…’ at the bottom of the box that comes up. You can then select ‘Special Characters’ at the top and either ‘Em dash’ or ‘En dash’ (at the very top of the list) and click on the Insert button, which will insert the selected dash wherever you have left the cursor in the text, so do be sure to position the cursor correctly before using this method. You will also find the shortcut keys for both kinds of rules by following this path. Word will automatically create en rules and em rules for you, however, if you key in the right information in the right order. For an en rule, type the word that should precede the en rule, add a space after it, type a hyphen (or two: see below), another space, the word that should follow the en rule and then a space after it. When this last space is added, the program will change the spaced hyphen into a spaced en rule, but it will not do this if there are no spaces around the hyphen or in some cases when the program detects what it considers something odd about the sentence structure or punctuation, so if you do not want spaces around the en rule or the program is not cooperating, you will need to use the Insert function as above or the appropriate shortcut key. For an em rule, type the word that will precede the em rule, then type two hyphens in a row without any spaces, followed by the word that should follow the em rule and a final space. Again, when the last space is added, the double hyphens will be transformed into an em rule unless the program decides that something about the sentence is odd, in which case you will need to use the Insert function or the appropriate shortcut key. You will also need to use one of these methods if you want a spaced em rule because, if you add spaces on either side of the double hyphens, Word will turn the hyphens into an en rule instead of an em rule.