How to Decline Pater Familiās?

What’s the genitive of pater familiās? Is it pater familiātis? patris familiātis?

Actually, it’s patris familiās.

The second word, familiās is an archaic partitive genitive, so it’s not declined.

  • pater/patris/patrī/patrem/patre/patrēs,etc. familiās.

However, if we’re discussing the father of many families…

  • pater/patris,etc. familiārum

The Essential AG: 43b