A lot of Norwegians don't distinguish 'da' and 'når', and only use 'når', which has been the bane of many Norwegian teachers. They might merge in the future.
'da' is used when it has happened in the past. "Da jeg var liten" = "When I was young".
'når' is about the future/repeating events. "Når jeg blir gammel" = "When I get old"(future) "Når jeg fisker" = "When I'm fishing"(repeating).
I forgot to mention which: It's 'når'. I'm not sure if this will ever happen, but because a lot of people use 'når' instead of 'da', it is only natural that it would be allowed some time in the future.
Sounds familiar hehe Like the English "who" and "whom" distinction. Linguistic evolution... frustrating in short term, fascinating in long term ^^
What about plain old present tense? Like in "When I leave..." can you use either, or do you have to use "når"? It seems that "da" is reserved purely for the past tense, but I just want to be sure. :)
"When I leave" would be about the future, it's an event that hasn't happened yet, or refer to a recurring thing, something you often do.
Notice that present tense is used in both these cases, as I did in my examples (blir/fisker).
»They might merge in the future.« So, it's gonna be something like "dår"?