Het eens zijn is an idiom, meaning to agree, so "Ik ben het eens met jou." is "I agree with you." :)
Was this idiom taught before? I was surprised there was no hint giving away the idiom like they usually put.
Literally - I am it one with you. Like 'being at one with' in English.
I've seen this with "er". Would that go immediately after het? (Ik ben het er helemaal met je eens)
That is not correct, you can't add "er" in this sentence. However, you can say:
- Ik ben het er helemaal mee eens - I completely agree (with it)
In that case you don't agree with a person, but with something that has been said. As usual, "with it" becomes the pronominal adverb "ermee", which can then be split up.
So, would the unconjugated form be "het ermee eens zijn"? (As het eens zijn is for "Ik ben het helemaal met je eens.")
Sorry, I meant "I fully agree with you". That's what I gave and I was marked wrong...
Would you say this to highlight that you wouldn't always agree with someone but you do in this case?
Would it be similar to saying "For once, I completely agree with you!" as if I said that in England, saying 'for once' implies that I wouldn't normally agree.
This sentence in Dutch is nothing close to that expression in English. Duolingo should not be introducing this using a modifier «helemaal» in its construction IMO.
Ik ben het oneens met jou. (I disagree with you.) Ik ben het eens met jou. (I agree with you.)
«еens» does NOT mean «once» in this expression (uitdrukking).
Also, «on» in Dutch can often be a prefix quite akin to the English «un».