"Have you received an answer yet?"
Translation:Har du fått svar än?
not sure why it does not need the indefinite article (ett) here - only chose 3 - not 2 and 3
I don't know the specific rules for this case. I've been trying to construct other sentences using other nouns than answer, and what I can observe is that an article is not required for words that are the same in singular and plural. That actually makes me think that it really is the plural form that is used, but with the interpretation being either singular or plural.
I could say "Jag har fått brev." Meaning either "I've got a letter" or "I've got letters.". I could also say "Jag har fått ett brev." to stress that it is exactly one letter. However I would not ask anyone "Har du fått ett brev?" because I don't care if it is one, ten or thousand letters.
The same reasoning applies to answers as well.
I think you are right. It was just an observation I made that I could not recall any noun with separate plural form that can be used in the singular from without an indefinite article after "Har du fått." unless it is a shorthand where you really mean another word. ("Har du fått sol" where sol really is short for "solljus")
These cases are indeed complicated. Your example with dikter somewhere else was interesting, I think people used to use dikt in the singular that way, but don't any longer, and now we have the same use of the plural indefinite instead. Maybe partly because it's really unclear whether these words are singular or plural. We had this problem early on when building the course, about the sentence Han äter ägg. We just translate it into He eats eggs, which is probably the best translation, but I wouldn't say that ägg is plural in the Swedish sentence anyway.
Don't know if anybody has written about this but if not, it could definitely be an interesting subject for a paper.
Dikt is a good find. I think that the old use you refer to actually would translate to poetry rather than poem, and could still be used. "Han skriver dikt" - "He writes poetry".
I've noticed several questions regarding the "Han äter XXX"-constructs. I interpret these as "XXX is part of his diet" or that he is eating any amount (from just a piece of to several) of XXX. But I think you are right in that this question is closely related to that.
And in relation to the food example fish is actually a very interesting word. Especially since both fish and fishes are plural forms in English but with different use. I'm not proficient enough to state if there is any relation between the two plural forms in English and the use of fisk as a collective in Swedish compared to the fiskar plural form.
"Jag har fisk i mitt akvarium." and "Jag har fiskar i mitt akvarium." have slightly different meaning. The first one states that "I actually use my aquarium for fish" while the second states that I have fishes in the aquarium.
There are several other nouns that, at least in terms of food, take the collective usage from the singular form. (hummer, kyckling, kastanj, ost, etc.)
Now we're getting fairly off-topic, but you might be interested that as a native English speaker I interpret fishes as meaning multiple species of fish, and don't know if I've ever actually seen it used outside that context.