It is indeed so the ghosts can cast rituals. I don't remember there being many of them that do that, but the possibility is there.
Great, thanks for the clarification!
(And yes, there were only three of them with that power, actually: Ierimyra, Pitsdim and Granorda).
I am running Calebais at the moment (in German with an English version 
) and bought this PDF based on this thread. Although I don't speak a single word Spanish I can highly recommend it, just because of the excellent illustrations!
You can buy digital versions now: holocubierta.com/market/mark ... /arsmagica