"What does he do with this?"
Translation:Wat doet hij hiermee?
Why can't we translate this sentence as "Wat doet hij ermee" instead of "wat doet hij hiermee".
The three words 'ermee', 'hiermee' and 'daarmee' all have slightly different meanings. 'Ermee' means 'with IT', 'hiermee' means 'with this' and 'daarmee' is 'with that'. It's the same for similar words with the prefixes er-, hier- and daar-
If I understand correctly, "jij" uses the conjugation for first-person singular (ik) when the sentence is a question.
So, why do we say "Wat doe jij hiermee" but keep the "doet" for "hij"?
The jij/je form of the present tense is the stem of the verb, 'doe' in this case, with or without an extra -t. The 't' is added when jij/je comes BEFORE the verb (e.g. jij doet het = you do it), but dropped when jij/je comes AFTER the verb (e.g. Wat doe je? = what do you do)
With the 3rd person singular (hij, zie/ze, etc), the -t ending is compulsory. As to why, it just is - sorry! Languages are confusing sometimes :(
That was the kind of "why" I meant, thanks :) I thought I'd picked up on that dropping the "t," but I didn't realize it was only for "jij/je."