Mind, Theater, Cave

Perhaps the most formidable challenge to Hume's metaphor of Mind as a theater consisting in no more than a sequence of images, is implicit in its best-known predecessor--Plato's 'Cave'.  In order to counter that challenge, Hume needs to explain how the sequence of events presented in the Republic, including the cave itself, is itself no more than part of an internal mental drama, i. e. how that sequence is not derivative.   Analogously, he needs to explain how his own 'theater' is part of the scenes that transpire within a theater.  Hence, entailed in his metaphor is either an infinite regress of theaters, or else an existence outside the theater, which would seem to contradict the fundamental premise of his theory of Mind.