  A second reply is reductionist, and it simply denies the slogan.  In other words, identity is not necessary for moral  responsibility. Instead (the reductionist could say), what matters is psychological continuity (or connectedness), regardless of whether it obtains uniquely. This allows the reductionist to handle the fission  case in the following way: while neither Y nor Z is identical with X, both are fully psychologically continuous  with him, and insofar as ownership of actions consists in  psychological continuity with the original agent, and because  ownership is the necessary condition for responsibility, both  Y and Z may be morally responsible for X's crimes.