Hyphens, En Dashes, Em Dashes

Q. Is the prefix “non” always used without the hyphen now? For example: nonresponse, as opposed to non-response.

A. CMOS style is to close up prefixes unless there is a reason not to. (Some editors leave the hyphen in to avoid doubling a letter: non-native, pre-exist, co-owner—the first two of which Webster’s closes up.) We use an en dash when the prefix goes with an open compound noun: non–United States citizen. And we use a hyphen when the prefix goes with a hyphenated compound: non-English-speaking.