In English there are four relative pronouns: that, which, who; and the genitive one: whose
You probably already know when to use which.
In Danish there are three relative pronouns: som, der; and the genitive one: hvis
When the relative pronoun is subject (as in "Jeg kender kjolen, der/som er dyr" / "I know the dress, that is expensive"), one could use either "der" or "som".
This does not apply if the word before the relative pronoun is "hvad" (what), "hvem" (who) or "hvilken/hvilket/hvilke" (which); then it must be "der".
If the relative pronoun is object (as in "Jeg kender kjolen, (som) du snakker om" / "I know the boy, (that) you are talking about); then it could be "som" or nothing.
The quick mnemonic rules
If it is "whose" in English, use "hvis" in Danish
If pne can drop out the "that" or the "who" in English, pne can keep it out in Danish or use "som"
"Hvad som", "hvem som" and "hvilken/hvilket/hvilke som" is bad Danish (or Norwegian); in these cases, use "der"
In all other cases, use either "der" or "som"
It is a used as subject, and it's not with "hvad", "hvem" or "hvilken/hvilket/hvilke"; therefore both "der" or "som" could be used.
But that contradicts what the info for this lesson says, which is that "der" can only be used for objects.
If I understand this right (please someone correct me if I'm wrong), both explanation forget to tell if it's object of the main clause or of the subordinate clause.
So, in the lesson, they are talking about the object of the main clause.
That is the girl who loved me. Det er pigen som/der elsket mig.
Here, det and pigen both refer to the same person (pigen is attribute to the subject det because være is a stative verb). 'der' only works if the subject of the subordinate clause is the object in the main one.
However, if the object in the main clause becomes the object in the subordinate, you get a construction similar to that in English:
That is the girl (that/whom) I love. Det er pigen, (som) jeg elsker.
'I run so that you lose weight.' (I run for you to lose weight.) is an example of sentence you cannot use 'der' with. But I guess this might not be the best illustration. Hmm I'm getting confused too. I can't seem to find an adequate sentence where the object in the main is not referred to in the subordinate. It makes sense to always find the main object in the subordinate, because a subordinate clause by itself is an object of the main clause. If someone can help me clear my grammatical thoughts, that would be great! ;)
Oh btw, I tried to translate one of my previous sentences into Danish, I'm not quite happy with the result. Can someone correct me?
[...] er en eksempel af frase med der kan du ikke bruge 'der'. (Is 'der' referring to 'frase' here?) [...] er en eksempel af frase du kan ikke bruge 'der' med.
I guess now you are left with more questions than answers, sorry! :/
Looking at the comment below from Kevin B, there seems to be a mistake in the lesson's Tips and tricks.
True, Sara! The sentence might be possible with the right context (it is, strictly speaking, grammatical), but I think it would sound more natural as "It's him there.," or "That's him there!" or "He's the one over there," or even "He's the guy there."
"So what is he going to do now?"
"I don't know. It is him who is there, who has to talk to the people, who has to deal with all the trouble. God knows, which decision he is going to make."
Since I cannot post comments on the lesson tips and tricks, I'll say it here. I think there is a mistake. 'Som' can be used as both subject and object (in the subordinate clasue) 'Der' can only be used as subject (in the subordinate clause)
"som" is the relative pronoun for both subjects and objects, while "der" can only be used for subjects (here, the difference is only in style). For further reading check http://sproget.dk/raad-og-regler/artikler-mv/svarbase/SV00000049 (in Danish) and/or look at the comments above.
Thanks for the answer, but that is what confused me because the Tips & Notes say something different: "som can be used for both subject and object, but der can only be used for objects." By subject and object, they mean the case? Or like person and non-living object?
You are right, I turned the sentence around by mistake, because I wanted to explain it differently in the first place... /o\ I corrected it now... So there is actually a mistake in the Tips & Notes and yes, subject and object refers to case, not to properties of the referees.
Now I'm confused. The der here refers to the object, ham, doesn't it? (Even though it's a cupola sentence, but Danish doesn't seem to care.) Det is in nominative and ham is in accusative, so it should make the former the subject and the latter the object.
Okay, thanks. Now I understand it, with "der" being only the subject everything is clear :) How can I report mistakes in the Tips & Notes section?