#12: Blog about the proper use of the hyphen versus the em dash.

Hyphens, which are narrower than dashes, should be used to break single words into parts, or to join separate words into a single compound (i.e. twentieth-century). Spaces shouldn’t be used before or after hyphens, except in the case of the hanging hyphen (the nineteenth- and twentieth-centuries).

Old-school style (note the hyphen use there) was to use hyphens with many prefixes (such as pre-school) but now-a-days (again, hyphen) most prefixes are not hyphenated (i.e. preschool). However, hyphens are required if you’re adding a prefix to a proper adjective (i.e. how very un-Canadian of him). Hyphens are also used with prefixes such as ex- (ex-boyfriend), self- (self-confident), all (all-encompassing), and with the suffix –elect (mayor-elect).

Generally, use a hyphen when:
1) joining two or more words together to serve as a single adjective before a noun (i.e. a one-way street, a well-known author) but not after the noun (i.e. the author was well known).
2) joining compound numbers (i.e. thirty-two).
3) avoiding confusion or an awkward combination of letters (i.e. re-sign the petition – so as not to confuse with resign).

The ‘en dash’, so named since it is roughly the width of an ‘n’, is slightly longer than a hyphen and is used for periods of time when you might otherwise use ‘to’. For example, I lived in Montreal during the years 1999–2000.

The ‘en dash’ is also used to contrast values or illustrate a relationship between two things. For example: mother–daughter relationship, Ottawa–Toronto flight, a score of 12–3.

The ‘em dash’, a dash which is the width of an ‘m’, is best for informal writing where it can replace commas, semicolons, colons or parentheses and indicates emphasis, an interruption, or a change of thought.