"He is speaking about something boring."
Translation:On mówi o czymś nudnym.
'something boring' in nominative would be 'coś nudnego' right? So why is it here 'czymś nudnym' instead of 'czymś nudnego'?
Hmmm. I believe that in most situations the whole phrase assumes the needed case. Although for sure there are situations when it doesn't happen, like with ownership: pies Adama (Adam's dog) -> On mówi o psie Adama. But then in that noun phrase the ownership is still identical, and the sentence would make sense as just "On mówi o psie".
I guess that you can also just substitute "czymś" with something specific and then you have a normal noun phrase: On mówi o nudnym wykładzie. And it's not surprising that this whole noun phrase assumes Locative.
This is more of a stream of consciousness than a real answer, but I don't have anything better ;)
Thanks. I thought that most languages with cases kinda work the same, but that’s clearly not the case. In Dutch, we sometimes have some remnants of cases (like ‘iets saais’ [something boring], which is genitive). As cases aren’t actively used anymore, this doesn’t change even though it’s in a different function. That’s why I somehow thought that it’s be like that in Polish as well, but I was wrong.