My answer was 'be at home until six', which was marked as correct, but 'be at home by six' was given as an alternative answer. As the implication from my answer is that someone is already at home, but the alternative answer is an instruction to somebody who has not yet arrived at home. How can they both be correct?
I would say that "be at home until six" isn't a good translation, but Duolingo is full of bad English translations accepted as correct, presumably because it's not only native English speakers who are learning and they're testing people's German and not their English ...
Exactly! I find this very confusing. How can they possibly both be correct? Imagine you're arranging for the internet company to come set up your connection and the employee on the phone tells you "sei bis sechs zu Hause"... obviously only one of the two meanings can be correct!
Don't "be home by six" and "be home until six" have the exact opposite meaning?
Be home by six: you can spend the time before six wherever you want. Just be home by six.
Be home until six: stay home until six and then you can go out.
And for the record, I wrote "be home until six" and was rejected by DL.
No. Imagine it's a guy cheating on his partner and he tells his lover: "be here at six (since my partner will be gone by then)". It would not be convenient if the lover interpreted "be here by six (any time before six is fine)"; the lover goes and shows up at three, only to find that the partner is still there! :0 ... they probably deserve it anyway... >=(