Dashes: hyphens, ens and ems

The hyphen is the most common device for linking words and word fragments. If in doubt about whether or not to use one, consult the latest edition of the Macquarie Dictionary or the Style manual for authors, editors and printers. Appropriate use often depends on context.

Use a hyphen:

• when using terms adjectivally, but not when using them as nouns: the decision-making process was protracted; this procedure expedites decision making; sustainable land-use practices; land use was variable
• when the last letter of a single syllable prefix and the first letter of the word are the same vowel: re-educate not reeducate; de-emphasise not deemphasise (however, cooperate, coordinate and their derivatives are no longer hyphenated.
• to avoid confusing a new word with one currently in use: he re-covered (put a new cover on) the book; he recovered (retrieved) the book ; she re-signed (signed again) the document; she resigned (relinquished) the document
• with co- (joint) and ex- (former), whether or not the attached word begins with a vowel: co-accused; co-worker; ex-admiral; ex-wife.

En rule (–)

Use an unspaced en rule, not a hyphen:

• to link spans of figures, time and distance: pp. 466–53; 1979–91; May–July; City–Toowong buses
• to show a link between words that retain their separate identities: the body–mind split; a north-south alliance; a copper–zinc alloy.

Use a spaced en rule if more than one word is to be linked on either side: the Queensland - New South Wales border; 16 BC – 70 AD; City – Fortitude Valley trains.

Do not use an en rule to substitute for and with the word between, or to substitute for to with the word from: the years between 1990 and 2005, not the years between 1990–2005; from 20 to 25 applicants, not from 20–25 applicants.

Em rule (—)

Use em rules sparingly to:

• link words that signify an abrupt change: We decided to go by air—a momentous decision under the circumstances.
• introduce an amplification: Global warming may have catastrophic effects—for example, causing the ice caps to melt and sea levels to rise.
• indicate parenthesis within a sentence: Her abrupt change of direction—this time to the north—left them mystified.