Breakdown of Hann veðjaði á rangan hest.
hann
he
á
onto / on / in (static location) / on (a day of the week)
hesturinn
the horse (m)
rangur
wrong
Questions & Answers about Hann veðjaði á rangan hest.
Why does the preposition á take the accusative case (rangan hest) here instead of the dative?
The preposition á governs the accusative when it implies direction or movement. Even though this is an abstract concept rather than physical movement, you are directing your wager onto the horse, so it triggers the accusative. If it were dative, it would imply the physical action of betting took place while you were sitting on top of the horse!
Is að veðja á rangan hest a natural Icelandic idiom, or just a literal translation from English?
It is a perfectly natural and widely used idiom in Icelandic that means exactly what it does in English: to make a bad choice or support someone or something that ultimately fails. Icelandic shares quite a few idioms with English, and this is one of them.
If I wanted to add an amount and say 'He bet 1000 krónur on the wrong horse', how would the grammar change?
The verb veðja takes the dative case for the amount being wagered. So you would say Hann veðjaði þúsund krónum á rangan hest. The thing you are betting on stays in the accusative after the preposition á.
Could I use vitlausan instead of rangan here, since both words can translate to 'wrong'?
While vitlaus is very common for 'wrong' or 'foolish' in everyday speech, this specific idiom is fixed. Just like in English, you must use the direct equivalent of 'wrong', which is rangur (declined here as the masculine accusative rangan).