  On the other hand, the nonreductionist might insist that I am  justified in having special concern for my future ego simply insofar  as it is the only thing that will be me, regardless of  whether or not Relation R is preserved by or within it. On this  account, then (what Parfit 1984, 228 calls the “Featureless  Cartesian View”), who I am – my essential identity  – is independent of any particular psychological properties.  But if identity is entirely prized apart from psychology in this way, and if the ego to be tracked is an immaterial substance (as it is, of course, on the Cartesian version), we are left with two related  puzzles. First, if the particular ego I now have (or am) can be  perceived or identified neither directly, via some empirical means,  nor indirectly, via a particular set of psychological properties it  might be thought to evince, then we actually have no reason to  believe that there is just one such ego unifying the various stages of our lives. Instead, our bodies might get a new,  qualitatively identical ego every year on our birthdays, or perhaps  every day, or perhaps there is a river of them flowing through us  from moment to moment. If this were to happen, then I would  cease to exist, replaced by a qualitatively identical person who then inherits my psychological properties. But no one would even notice!  This would be rather odd, to say the least, and this is because of  the connection we think should obtain between our metaphysical  criterion of personal identity and our epistemological criterion of  personal identity. In other words, we tend to think there is a close  connection between the nature of personal identity and what enables  us to determine when identity obtains. So if what makes  X and Y identical is sameness of body, it will also be our reidentification of that body which enables us to determine  that X is Y. Similarly, if what makes X  and Y identical is some kind of psychological continuity,  then determining that X and Y are identical will be a matter of determining whether psychological continuity obtains  between them. Now in both the body and the psychology cases, we have  the capacity to do the tracking in question. If the Featureless  Cartesian View is correct, though, we do not. We cannot track  immaterial egos floating free from any particular psychological  properties, so on this view we would never be justified in claiming  to have reidentified anyone, nor would we be justified in claiming  special concern for some future stage of our bodies: in both cases,  we could have no reason whatsoever for thinking that the persons in  question were who we thought they were (Perry 1978, 6–18; Parfit  1984, 228).