I'm not sure if this is correct, but I seem to --maybe!-- have sorted out using på: if I can use "during" instead of "in", or at least the concept of during ("in" being as damnably versatile a word in English as på seems to be in Swedish), I can use på.
In the afternoon = during the afternoon = på eftermiddagen I swim on mondays = I swim during mondays = Jag simmar på måndagar
"I" seems to be much more definite: this afternoon = i eftermiddagen today = i dag the morrow (yes, I know it's archaic) = i morgon
Good crickey, I can't seem to get a grasp on it otherwise and I'm at my wit's end. I might as well toss i, om, på, and half a dozen other words into a sack and choose one at random. Even if I have pinned down "på" and "i," even a little bit, "om," "av," and "till" are still mysteries utterly beyond my ken.
Ye gods, I hope my intuition spins up soon and I begin to understand these slippery little beggars.
This is largely correct. :)
Two minor things:
- It's i eftermiddag rather than i eftermiddagen
- I'd translate i morgon literally as "to-morrow", since that is exactly what it means and is closer grammatically to its English cognate
Prepositions are easily the trickiest part of achieving fluency in any language, so don't get discouraged. We all struggle with them in one way or another.
Thank you --and about i eftermiddag... Oops. Clearly I have a ways to go.
In English (perhaps only American-English?), an alternate yet archaic phrase (but still somewhat common in the region where I grew up) is "the morrow," meaning "tomorrow." "I'll see you on the morrow" = "I'll see you tomorrow." In that phrase, the definite-ness of "the morrow" seems to fit with using "i". Perhaps? Maybe?
I'll stick with it.