Up to where P1 says, "Therefore, Korean has an independent origin from Chinese.", that is indeed argument from ignorance. Where P1 offers some discussion of di

Up to where P1 says, "Therefore, Korean has an independent origin from Chinese.", that is indeed argument from ignorance. Where P1 offers some discussion of differences between Korean and Chinese, that's where we start to get into a discussion based on evidence that can be evaluated. If P2 doesn't find it convincing, then we can ask why; this allows P2 to muster evidence which can be evaluated. That's a fine and constructive direction. A finite conversation like that doesn't necessarily end with a solid conclusion and everyone being convinced of the same thing. What you're pointing out with regards to the perceived strength or weakness of certain assumptions is not what we're talking about with argument from ignorance: argument from ignorance is about the form, not the semantics.