I know a son of Kateřina. Why not. Maybe Kateřina has two sons. Proč nemůže být a son? Katečina může mít dva syny. Thakns :-)
Your suggested English sentence, "I know a son of K", is equivalent in English to "I know one of the sons of K".
But that is not what the Czech sentence says. The Czech implies that K has one son. (Or am I mistaken?)
The correct English is therefore "K's son" = "the son of K'. English idiom requires the "the" if you use the latter form.
How would we translate into Czech "I know one of the sons of Kateřina"?
I am guessing, but perhaps: "Znám jednoho synů Kateřiny."
Someone please correct me if I'm wrong.
Here, syna is the accusative, as the direct object of the verb. The genitive and accusative singular forms of syn are the same. But Kateřiny is genitive (son OF Kateřina).
Weird question but... Could Kateřiny also be accusative plural and syna genitive singular?... does this mean that in a very specific context this sentence could mean "I know the son's Kateřinas"?