For once—mark this, youngsters, Mr. John is being kind, or close to it—I find no fault with the Associated Press Stylebook. Its entry on non- is relatively straightforward:

non- The rules of prefixes apply, but in general [emphasis added] no hyphen when forming a compound that does not have a special meaning and can be understood if not is used before the base word. Use a hyphen, however, before proper nouns or in awkward combinations, [emphasis added] such as non-nuclear.

Oddly, some copy editors appear to have registered no hyphen when forming a compound, fixated on it, and blanked out the rest. It may have something to do with the regrettable tendency within the craft to prefer Rules, however illusory, to judgment, however variable. But AP makes it unmistakable that judgment is to be exercised.

I’ve ridiculed nonlife-threatening in the past and have apparently broken the staff at The Sun of threatening nonlife. Sometimes they even lapse into English and write that “injuries were not life-threatening.” But the other day I saw someone identified in edited copy as a nonpresident.

Maybe I’m wrong about their misinterpreting the stylebook. Maybe they just think that part of the cutbacks is a rationing of hyphens.

Anyhow, whatever dictionary you happen to use should have an extensive display of non- compounds, some hyphenated and many not. You can look things up or not, depending on whether you have the time, but here is a little guideline for non- compounds: If it looks odd without a hyphen, or you think the reader might stumble over it, put a hyphen in. Even if the dictionary shows it as solid. It’s less likely to be distracting with the hyphen than without.

If you’re not non compos, you should be able to handle that.