Hyphenation in "first century AD" etc as an adjective
I edit a lot of articles that contain phrases such as "A first century AD inscription..." or "First century BC writer Herodotus..." I know that a compound adjective before a noun is usually hyphenated, so if the phrase were just "A first-century inscription" I would hyphenate accordingly, but "A first-century-AD inscription", despite seeming grammatically correct, feels somehow wrong (I think because of the abbreviation) and I don't recall ever seeing this used. Meanwhile, "a first-century AD inscription" I'm fairly sure is ungrammatical.
So to sum up, which should it be?
- A first century AD inscription
- A first-century AD inscription
- A first-century-AD inscription
Many thanks.
Every permutation of the sentence you provided is grammatical.
Your question is really just about style. Hyphenation is about so-called convenience, the communication of a phrase that becomes more understandable (less open to ambiguity) because of the hyphenation.
The essential question is, will anybody be likely to misinterpret the sentence if it's not hyphenated? If not, and if hyphenating it in some way looks wrong, then don't hyphenate it.
On the other hand, if you follow a style guide that says to hyphenate it specifically, then do that.
My personal opinion, which is not in any way definitive, is that if you're going to hyhenate first-century, you should also add hyphenation to the AD part.
Not only would it be consistent, but it's possible there could be misinterpretation if you don't. You could be talking about a first-century [AD inscription]—assuming such a thing existed.
So, I would choose to either hyphenate all three words (and perhaps have it look a little strange even though not open to any misinterpretation) or none of them (which might look better and would very probably not be misinterpreted). But that's not to say that you should make that choice.
I recommend the one-hyphen approach:
- a second-century BC inscription
- a second-century BCE inscription
- a fourteenth-century CE illumination
In each of these cases, the era is really acting as a little parenthetical that just happens to be denuded of its punctuation. If you were to spell out the abbreviated phrases while using them in the adjective form, the grammar would collapse. Since you can't discard BC or BCE without causing confusion, it's best to just let them float as inconspicuously as possible and not try to shoehorn them into the adjective with hyphens.
With that said, I remain on the side of the traditionalists who advise against using AD in this capacity, regardless of how hyphens are deployed. The argument is that the phrase Anno Domini has a specific unit of time built into it—and it's years. It's perfectly reasonable to say AD 1337 (or 1337 AD if you must), but to say fourteenth century AD is to say fourteenth century year of the lord, which is clearly nonsensical. (The good news is that this is a language fight that rarely needs picking because the present era usually doesn't need to be specified, and in the contexts where it matters CE is probably an acceptable or preferable substitute.)