I have not read Kaplan's book--yet.  I agree with Hal that we
should not become fixated on duality.  Yet, I do believe we need to keep
this approach to Twain open as a useful means for understanding the
man--if not his work.  This idea of a dual nature did not arise with
Freud, or Nietzche, for that matter, with his Apollonian and Dionysian
separation of human personality.  I suppose Plato and Aristotle had
something to do with this notion of duality, two realms of existence and
such.  Perhaps the perspective pre-dates the Greeks.
        Personally, I find understanding what I see as Twain's divided
self to still be a fascinating project.  No need to abandon a model that
has yet to be fully developed and provides, I think, one of the more
fruitful paths into the mind--and spirit--of Mark Twain. Twain is surely
a singular fellow but not necessarily a singular personality.

Jason