Modifying phrases are hyphenated when used before a noun, but not after — unless the hyphen is needed to prevent confusion:
- He was a well-known man.
- He was well known.
- She has a full-time job at Brown.
- She works at Brown full time.
Words formed with prefixes (nonprofit, predate, pre-existing) are only hyphenated to avoid duplicate vowels and consonants.
- anti-inflation
- shell-like
- pre-empt
Two or more hyphenated modifiers having a common base are treated in this way:
- long- and short-term memory
- two-, three- and 10-minute intervals
Do not use a hyphen after words ending in “ly” followed by a participle or adjective:
- poorly attired man
- historically underrepresented group
Use an em dash (—) sparingly to indicate emphasis or explanation, to define a complementary element or to denote a sudden break in thought. Put a space on each side of an em dash.
- The influence of three impressionists — Monet, Sisley and Degas — can be seen in his work as a painter.
Note: On an Apple keyboard, form an em dash by selecting option+shift+hypen. On a PC select Alt+0151.