Alatius wrote:The etymology of "på" is a bit interesting. The original form of this preposition was simply this "å" that you have noticed. It is related with the English "on". And just as in English, it was often used in the combination "uppå" ("upon"). But what happened was that this word started to be perceived as "upp-på" instead of "upp-å", and then people started to say "på" even without the preceding "upp". (Imagine, if you like, an alternative history form of the English language where "pon" is the regular preposition, and "on", to the extent it is used at all, sounds quaintly Victorian!)
What about Danish and Norwegian? In the former, the preposition is definitely also på, and is used the exact same way as in Swedish. Or did the change you were talking about occur before Swedish and Danish split into two separate languages?
Or was it initially å in Swedish, but på in Danish? Actually the preposition по exists also in Bulgarian and Russian, with slightly different but similar meanings. Russians even say по-русски the same way Swedes say på svenska. We don't do that, but we might say по пътя за вкъщи as a Dane might say på vej hjem.
These are my observations without any factual knowledge of the origin and evolution of this preposition in these languages - maybe somebody else could explain the link between them or lack thereof?