Hyphenated prefixes

AMA style says that common prefixes shouldn't be tacked by hyphen to foundation words. Anti- is one such common prefix, so you wouldn't write anti-microbial with a hyphen, as if the prefix carried its own weight or idea, but antimicrobial, a single, elegant word.

This is not, of course, a ban on using hyphens with prefixes. When a common prefix is paired with a proper noun (anti-English), for example, a capitalized word (non-Darwinian), an abbreviation (post-HIV), or a number (mid-1900s), then tack away. But generally the rule is no hyphens with common prefixes: coauthor, deidentify, interrater, midaxillary, nonnegotiable, overproduction, postamputation.

If this sounds too easy, give yourself a pat on the back. It is too easy. Regular readers of the Journal of the American Medical Association (JAMA) will have encountered inexplicable exceptions like microRNA, which, based on the AMA rule, should be hyphenated as micro-RNA. And in truth, the hyphenated version can be found on JAMA's Web site too, but microRNA is the (anti)rule.

Post- is another common prefix that deserves mention as an interesting and notable exception. Under the heading When Not to Use Hyphens, AMA lists posttraumatic as an example of the rule that common prefixes are not joined to foundation words with hyphens but combined instead. Right. Got it. The trusting writer or editor applies that rule to posttransplant, postresection, or postsurgery, but it's not always correct to do so. Sometimes it's flat wrong.

It's true that post can appear as a combining adjectival prefix, and when it does you fuse the words and use no hyphen, as in posttransplant recovery. But if you're trying to say that Mr Smith's condition improved post transplant, then post is not a prefix at all but a freestanding adverb. So there are plenty of contexts within which you'd need to write post resection, post surgery, or post partum, where post is its own word, carrying its own content, standing on its own descender.