The Humble Hyphen
http://www.stc-carolina.org/tiki-index.php?page=Humble+Hyphen

Wenger, Andrea
Carolina Communique
2006

Abstract:

The hyphen serves a single function. It joins things together: syllables of a word separated at the end of a line; two words used as a compound; or a modifier and the word it describes (when the combination itself is used as a modifier). But for the latter two functions, a hyphen isn't always needed. So how do you decide?