"Next month is April."
Translation:Następnym miesiącem jest kwiecień.
because with "jest", but without "to" you need one noun in instrumental.
So "następnym miesiącem jest kwiecień"
or "następny miesiąc jest kwietniem"
are both gramaticaly correct, but it is more common to use kwiecień as subject and next month as object.
and I would personally say "następny miesiąc to kwiecień" 99% of time
"Następny miesiąc jest kwietniem" is still not accepted, but thanks!
Well, I hope you do indeed start to grasp it :) Just to comment on the farmer sentence: it's strange, but possible.
"Mój ojciec jest rolnikiem" = My father is a farmer ('farmer' is the new information)
"Rolnikiem jest mój ojciec" = something like "The person who is the farmer is (actually) my father" -> You see several people, and you have to say which one of them is the farmer, and you say that it's your father. Okay, seems stranger than when I started writing this :D Let's try something more probable:
Lokaj jest mordercą. (The butler is the murderer) - you know that there is a butler, and now you're saying that this butler killed someone.
Mordercą jest lokaj. (The murderer turns out to be... the butler!) - you know that there was a murder, and now you're saying that the person responsible for it is the butler.
It's hard to explain, although I'm totally sure that "Następny miesiąc jest kwietniem" is just wrong. I'd say that the situation isn't like "Next month = April". "Next month" is relative to what we have now. We cannot define it as being April. April just happens to be the next month right now, in March. Well, in this sentence they clearly have March now.
But also, from 'when we are standing', April can be defined as 'the next month'. So "Kwiecień jest następnym miesiącem", or, what sounds better to me, "Następnym miesiącem jest kwiecień" (if put at the end of the sentence, April becomes 'new information', so at least this way this sentence makes sense).
The more I look at this exercise the more I think that I would just never say "Next month is April" in any way...
I don't know if it will be helpful, but some 'kinda similar' examples are shown in Part 1,5 here: https://www.duolingo.com/comment/16373167
I'm not sure I understand what you are getting at here. Simply thinking of the English sentence that would translate this, I could think of contexts that would call for both combinations. "Next month is April" could be a response to someone wondering why I was getting my financial papers in order (US income taxes are filed in April). "April is next month" might be something I would say if I saw someone writing April on the date line of a document when it was still March (perhaps forgetting that March has 31 days). It seems clear to me that the use of the instrumental case after the copula "to be" may limit the possibilities in Polish, but up to this point, it had always appeared that it simply meant the noun after the copula had to be in the instrumental. Could I, for instance, say "Rolnikiem jest moj ojciec"?