Comment by abraxas
I'm not a linguist so I can't send any articles that explain the origins of this mess. But here are actual examples of usage:
dwa ptaki (two birds)
dwoje ludzi (two persons)
dwie dziewczyny (two girls)
idę z dwiema dziewczynami (I'm walking with two girls)
dałem kwiaty dwom dziewczynom (I gave flowers to two girls)
kanapa dla dwojga (a sofa for two - gender unspecified)
dałem śniadanie dwojgu (I served breakfast for two others)
dwójka to słaba ocena (two is a poor grade)
dwie dwójki to razem czwórka (two twos are four altogether)
dostałem dwójkę z Fizyki (I got a two in physics)
z dwójką przyjaciół poszliśmy do klubu (we went to the club with two friends)
w autobusie dwójce siedział pijany facet (there was a drunk fella on bus number two)
O, dwójko, nie wracaj już do mojego dziennika (Oh, two, don’t come back to my gradebook again)
Of course I don't consciously think about when to use the right conjugation. I just know it by heart and it's second nature but I can only give coherent rules to some of them.
> I'm not a linguist so I can't send any articles that explain the origins of this mess.
It's probably because Polish, unlike English and most Western European languages, has a case system (where nouns are modified to indicate their function, i.e subject, object, instrument, etc).
That's a pretty common feature in grammatically conservative Indo-European languages. Other living Indo-European languages, like Lithuanian, are even more conservative and have preserved nearly the entire case system of their ancestor.