  Once we make the switch from talk of identity to talk of unity  relations as being ethically significant, however, things can also  get quite complicated. For there seems no reason in principle why two of the contending intrapersonal unity relations – psychological continuity and connectedness – could not also hold  interpersonally. That is, not only could psychological  continuity, say, hold one-many, between me-now and more than one  person in the future, but it could also hold between me-now and other spatially distinct, simultaneously-existing persons (Brink 1997a,  141–143, 1997b, 125–128). And the same could be true as well of  psychological connectedness. At least  some of the psychological relations making up connectedness and  continuity can obviously obtain interpersonally, e.g., sameness of  beliefs/desires/goals, and resemblance of character. But it also  seems perfectly possible that memories and intentions may be shared  between persons, produced by some common cause (Ibid.).  Recognizing these connections widens the boundaries of what counts as a targeted unit (and in so doing it may also blur the boundaries  between prudence and morality), but the ensuing messiness may not be  worth it. After all, if the proper ethical unit is a self, say,  unified by psychological connectedness, which obtains by degrees,  that means that my unity with many others – and with future  stages of myself – will be only partial, obtaining to various  people in varying degrees. But if these are the units targeted by  ethics, how do we mark their boundaries such that the moral concepts  and principles coherently apply (McMahan 2002, 62)? In addition, who  exactly would the practical agents in question be, where people are  more or less unified with each other (Brink 1997b, 113–114)? And  there may also be worries about how to apply moral concepts admitting of no scalar dimensions – like promises – to moral units  – like selves – that do (Williams 1976, 202–204). These  questions (and more) pose genuine challenges for accounts allowing  for interpersonal unities.