> > But either way, I don't see how a term like "greater" can apply to either without being defined more specifically.
>
> Yes, i'm a Christian. Yes, i grew up reading C. S. Lewis. Yes, i got to take a couple of philosophy classes in college (specifically, Intro and History of).

I knew all this, but it still doesn't clear it up for me. "Greater" means "more than." If you use it, therefore, the natural question is "in what way?" I could assume you're coming from a moral standpoint and saying that good is holier than evil (although that's sort of implied by definition) or preferable for the perpetrator or something, but that does not seem to fit the context of discussing the ability of good and evil to exist apart from each other.

"More powerful" might be what you mean, but that's still too vague. More powerful how and when? Certainly when I look around in the world today, I see that evil is the more powerful of the two, though I do believe that this is only because God has postponed his judgment on evil for now.

But something like "If evil cannot exist without good, good must be greater than evil" seems to me to be too broad as to be inapplicable. I can think of a number of ways in which good might be considered "greater" than evil, or even vice versa (when speaking of human moral strength), but none that depend on how they co-exist. Either they do, or they don't, by their own definitions.