Hyphen problems are now one of the twenty most common surface errors in student writing. The confusion is understandable. Over time, the conventions for hyphen use in a given word can change (tomorrow was once spelled to-morrow). New words, even compounds such as firewall, generally don’t use hyphens, but style manuals still differ over whether to hyphenate email (or is it e-mail?). And some words are hyphenated when they serve one kind of purpose in a sentence and not when they serve another.