Partial twinning and the boundaries of a person

Abstract

In special cases of partial twinning, two heads, each supporting a more-or-less normal human mental life, emerge from a single torso. It is often argued that there must be two people in such a case, even if there is only one biological organism. That would pose a problem for 'animalism', the view that people are organisms. The paper argues that it is very hard to say what sort of non-organisms the people in such cases would be. Reflection on partial twinning is no more comfortable for those who think we're not organisms than for those who think we are. We may have to accept that a single person could have two separate mental lives.