Explaining Locke and Leibniz

According to Locke, personal identity consists in psychological continuity (review KT 250-255).  I have argued in class that this position is vulnerable to the duplication argument: God, or some unknown process, could bring about a stream of consciousness that is qualitatively identical to your stream of consciousness; given Locke’s premises, this psychological duplicate would also be you; but that’s not possible.  (Assume for the purpose of this paper that personal identity requires numerical identity).

Leibniz’s theory of personal identity, with its heavy metaphysical commitments, is not, I have argued, vulnerable to the duplication argument.  Explain the role of the following concepts and principles in Leibniz’s theory of personal identity: the “complete or perfect notion” of an individual spiritual substance (review KT 151, 155-158); the Principle of Sufficient Reason (PSR) and the Identity of Indiscernibles (II) (review KT 174-175).  Then, explain why Leibniz’s theory is not vulnerable to the duplication argument.  Finally, explain which theory of personal identity you find more plausible:  Locke’s, with its light metaphysical commitments but vulnerability to the duplication argument, or Leibniz’s, with its heavy metaphysical commitments.