Now, this is a fairly minor issue and I also see it as something easily done. Though I am just guessing.
As it stands, Dark Knights are casters who carry a mix of both the typical casters/communers.
I was thinking about it as I drove home today, "What other casters get summon?" Then I began to think about the Anti-Dark Knight. The Paladin. They are communers, which carry a similar mix of spells as DK's... Just the opposite.
Why are DK's casters and not communers? They are definitely a zealous class. Their main spell "malform weapon" is completely based on religion.
So I propose, just to add a more religious feel to the class, that they be changed to communers. The ONLY drawback that comes to mind is that Silence will not affect them anymore, but blasphemy will now be the damaging spell.
What does that mean for DK's? It means DK's will not be able to silence eachother. It also means DK's will be weakened, because blasphemy is much more common than silence.
What does everyone think?
