"I see a calendar on the wall."
Translation:Mi vidas kalendaron sur la muro.
I put "en la muro" and it was rejected because it wasn't "sur la muro."
Shouldn't "en" be allowed here? I mean, the reason I didn't use "sur" is because I'm not literally putting the calendar on top of the wall. So I thought "en" would work nicely.
But apparently DuoLingo doesn't agree with me (at least, not yet).
In English, yes, but it's not actually ON the wall (on top of it) -- that's where the roof is. It's actually IN FRONT OF the wall.
"On" really only works for horizontal surfaces (on the floor, on the table).
Using it for walls is idiomatic and might not be the same in other languages. (It wouldn't work in German, for example -- things are not "auf der Wand" (on the wall) but rather "an der Wand" (at the wall).)
It seems to work well in Esperanto too, and probably for the reason given by mihxal.
https://www.tekstaro.com/ gives multiple exemples, including this one, with pictures instead of a calendar, from the Fundamenta Krestomatio
La pentraĵoj sur la muro estis bone koloritaj litografaĵoj
I don't know how to link the actual results page, but it mentions plenty of cases of "on the surface of the wall" ☺