[quote=Nocturnia]
Well if needed I can always just make Divine Area the active of sonar.EDIT: Though I'm curious as to why that rule would be in place, doesn't it make more sense to develop one ability rather then learn a new one?
[/quote]

you're not actualy learning a new ability. an active is adding special Radian Mana to the ability itself, enhancing it in powerful and sometimes unforeseen ways. Charles uses Radian Mana to increase his connection with Sophia and increase his stats.