Mulder-21 wrote:So, I wanted to ask, if any (or all?) language using the vocative, has some grammatical function, e.g. prepositional governmentation or similar, which requires the vocative.
In colloquial Polish the vocative form is sometimes used instead of the nominative.
Krzysiu / Jasiu / Kiesiu to dobry chłopak.
Krzysio / Jasio / Kiesio is a good lad.
Ten gościu przyszedł.
That guy came.
But this is restricted to some masculine nouns. Moreover, this only occurs in some regions of Poland.