word choice - Difference between ～だろうと and ～でも

Is there a major difference between ～だろうと and ～でも constructions in nuance? Can ～だろうと only be used with question words? I've seen any volitional followed by と for an effect like ～ても, but usually only with question words. Do the ～だろうと type constructions sound more or less formal?

Answer

Is there a major difference between ～だろうと and ～でも constructions in nuance?

In nuance, no, not really.

If anything, 「～だろうと」 would certainly sound more eloquent than 「～でも」. 「～でも」 could sound kind of blunt or unrefined when used to mean 「～だろうと」.

Can ～だろうと only be used with question words? I've seen any volitional followed by と for an effect like ～ても, but usually only with question words.

No. 「～だろうと」 can directly be preceded by regular nouns as well. Unlike 「～と」 and 「～ても」, however, 「～だろうと」 cannot be preceded directly by verbs for the meaning we are talking about.

An example with no question word used:

「[日本人]{にほんじん}だろうと、[外国人]{がいこくじん}だろうと、[消費税]{しょうひぜい}は[払]{はら}わなければならない。」

= "Whether a Japanese citizen or a foreigner, you must pay the sales tax."

Do the ～だろうと type constructions sound more or less formal?

Not necessarily. The phrase 「～だろうと」, all by itself, does not make the sentence "formal", but it does sound more formal than 「～でも」.

FWIW, we have a 「～であろうと」, which is definitely more formal than 「～だろうと」.