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.