In constructions like "det regnar" (it's raining) and the like, where a subject is needed, Swedish always uses det. This works the same way with a demonstrative pronoun like det här. That's why it does not and does not have to agree in gender.
Does that help to clarify?
I know this is an old comment but I'm still a bit confused. I've read multiple comments in multiple discussions that say pretty much the same thing as this comment, and it seems pretty straight forward, along with how you're supposed to use det if you don't know the gender of the noun it's referring to, or if the thing you're talking about is new to the person you're talking to (right?).
But sometimes when I translate a sentence in Swedish and follow these rules, my sentence gets marked wrong and Duo crosses the det out and tells me I should have used den instead. It doesn't happen all the time though, so I guess I'm applying the rules correctly in some cases but not in others? But I can't seem to see any difference between the ones that are marked correct and the ones that are incorrect (I wish I could remember an example, but I can't).
It's come up in sentences that are similar to Den är en bil (not specifically this sentence) even though, as I understand it, you would only use den är if you were either pointing right at the car or if you had already introduced the car in the sentence or clause preceding the one starting with den är. So, since I only have the one sentence to base my answer on, I would use Det är en bil instead, but sometimes similar sentences have been marked wrong because I used det instead of den and that has been very confusing.
So I guess what I'm asking is, when exactly are you supposed to use den? When would we ever use den är or den här in our translations if we don't have any additional context?
I feel silly for still not understanding this even after all the comments I've read that explain the concept. Sorry for the really long comment, it's difficult to explain something that is confusing to me.
Oh, you have nothing to apologize for. Swedish can be strange, and I'll do my best to explain. :)
Most often, it has to do with whether or not the thing referred to is introduced or not. If it is, it has to agree in grammatical gender (den/det), but if it isn't it defaults to det.
Jag har en ny dator. Den är väldigt bra. = I have a new computer. It is very good.
In this sentence, we're explicitly referring to a computer and nothing else, and thus we use den to agree in grammatical gender.
Filmen som vi såg? Den var tråkig. = The movie that we saw? It was boring
Again, we're referring specifically to an en-word (film).
Does that help at all?
I understand, but what's confusing me is that the course has told me I should have used den instead of det in sentences where there was no qualifying statement that introduced the gender of the subject that det/den was meant to be referring to. So in the context of the course, where at this point we're just given single sentences to translate, the vast majority of the time we should be using det because in the vast majority of sentences, the thing we're referring to hasn't been previously introduced in that context, right?
So, I've been asked to translate a sentence structured like "It is a car" and sometimes it will accept "Det är en bil" and sometimes it will mark that wrong and tell me I should have written "Den är en bil" even though the car hasn't been introduced yet, and previously it had accepted sentences like "*Det här är min syster" which follows the same basic grammatical structure.
It's the inconsistency that's confusing? I wish I had written down the actual examples of when this has happened, but it has been very simple stuff with no other qualifying statements, like This is my sister or It is a car. So when presented with a single English sentence like This is my syster, I would translate that as Det här är min syster, right? So why would the course sometimes specifically ask me to use den in the context of a sentence like that? Am I missing something here? Because that's quite possible.
[Edit: Also, thank you for the very quick reply! I appreciate it :)]
Without examples, I'm afraid I don't know why it is that you were asked to use "den". In ambiguous cases, both should work and if they don't, report it. You're right, however, that generally when something hasn't yet been introduced or if you're talking about something in general, "det" is used.
There might be some inconsistent sentences in the course, due to the human factor. If it happens again, feel free to take a printscreen and write to me here and I'll try to explain why things behave the way they do.
The closest thing in the course I can think of are sentences like Den här bilen är röd 'this car is red' where you'd have to use den här. Other than that, what Zmrzlina said. If you find anything like 'Den är en bil', report it immediately and preferably take a screenshot. Sentences like that are not accepted in the course so that would be a bug.
I can add an example
"Den här boken är konstig" Why is this sentence any different from "Det här är min fru"? In both of the cases the sentences are given by themselves, thus we don't know what the "den/det har" particle is referring to until the end of the sentence. I don't understand why in the first case we are allowed to use den but in the second case we are not.
Fear not, Captain Swede is here!
Saying "Det är min fru" is a normal sentence to mean "it's my wife" . Imagine a friend and you hear someone's coming and they ask you who it is. A perfectly good answer is "det är min fru".
Saying "Det här är min fru" sounds normal, like saying "This is my wife" when introducing her.
Saying "Den här är min fru" sounds very worrying. It's like you're saying "This one is my wife" as if you had to point out the difference between her and some other object of yours.
Does that help?
In this sentence, det här is the subject, corresponding to this in English. The noun is not part of the expression in this case. You're not saying 'this wife'.
If you say this house, then it would be det här huset or detta hus, in that case the noun would be a part of the expression. So it depends on what you're using it for.
This is my wife - Det här/Detta är min fru.
This woman is my wife - Den här kvinnan/Denna kvinna är min fru.
Hope this helps?