Subject and object. English is strange in this aspect, having merged singular and plural. Swedish, however, has not done so. The difference is the same as with I and me. One is subject, the latter is object.
Jag tycker om dig = I like you
Du tycker om mig = You like me
Ni tycker om mig = You like me
Jag tycker om er = I like you
Does that help?
The voice is not quite perfect on this sentence, as of May 10th, 2018, so I've taken the liberty of re-recording it.
In this case, the error isn't huge. But tycker om is a so-called particle verb in Swedish, meaning that it's one verb consisting of multiple words. If you leave either word out, the meaning usually changes completely. And hence, stressing the right word is important. Almost always, this means putting the stress on the particle - the om, in this case. The automatically generated voice has a tendency to put the stress on tycker instead, which is never correct, or on the word after tycker om.
Please find a correct recording on http://duolingo.vydea.io/368c899ce2294d01b421386934738810.mp3
For more info on re-recordings, please check the info thread: https://www.duolingo.com/comment/23723515
Thanks for listening. Ha en bra dag! :)
There are a lot of so-called phrasal verbs where a verb and an article/preposition belong together with a meaning of their own. English does this too. An example would be the sentence "I can't put up with this" where the verb and the preposition have a certain meaning. The verb tycka om works the same way. Just like you can't say just "I can't put with him", you can't say just "Vi tycker er" either.
Since "er" can be "you (plural object)" or "yours (plural possessive)", how would one distinguish between the phrases: "We like you." (e.g., We like the people.) and "We like yours." (e.g., We like the stuff the people have.). Or do you just have to work it out from context?
I'd say context. I can't really imagine a situation where this would be ambiguous. Maybe if you wanted to clear up ambiguity, you could say a noun after "er", so people will know that it means "your".
As a side note, imagine what English learners would think when they learn that 3 words--there their and they're--are all pronounced the same!
In a related kind of thing, my friend came back to school after missing a week because he was sick. I said "you're back!" And he replied "what about my back?" :D
'Vi' and 'er' in this case are unrelated. 'Vi' is the subject and 'er' is the object of 'tycker om.' It could've been anything. Vi tycker om honom. Vi tycker om jordgubbarna. Vi tycker om bara en jordgubbe. Likewise, it could've been any subject. E.g., Jag tycker om er. De tycker om er. Ni tycker om er. <== note that here we have you (pl.) in subject and object form in the same sentence. I hope that helps.
How do you know that "We like you" translates to "Vi tycker om er" What part of the english sentence of three words gives any indication at all that "you" refers to a multiple "you"?
I imagine that I've met a group of people and one person speaking for the group looks at me and says We like you, VI tycker om er. I would look around and wonder who else I'm with.