The philosophy of identity asks a simple question. What makes me, me? It’s valuable because it’s answer has a lot of implications:
- Whether killing one of two identical simulations with billions of identical people is murder or not
- Whether me today is the same person as me tomorrow (if not, the non-identity problem kicks in)
- Whether uploaded minds are the same as the physical person they were uploaded from.
- Whether sufficiently similar people count as one person.
There are a few basic theories of identity.
The first theory is naive physicalism. Who I am is defined by the physical vessel I inhabit. I am me because I have my body. The problem with it is that it’s highly counterintuitive in a number of situations. It says that if I transplant my brain into a cyborg body I am not longer me, which seems wrong because I am the same consciousness with the same memories and thoughts and feelings. It says that if I loose an arm, I am less me and if I loose enough of my body I am not me. It doesn’t really make sense.
The second theory is continuism. This is the one most people hold. It says that I am me as long as there is a continuous line of consciousness. Even though in 20 year I may be very different from myself today in a number of ways, I would still be me because there is a continuous consciousness that links those two points in time. The problem with this theory is that it’s also counterintuitive. If over the course of 20 years I gradually metamorphosize into a fish with an effective human IQ of 0.5, continuism says I’m still the same person. That seems wrong. A goldfish is not me even if it’s consciousness is directly linked to mine by an unbroken line of experience. There are also other weaker objections about things like interruptions in consciousness caused by, say, sleep or dying and then receiving CPR.
The final theory, and the one that best aligned with my intuitions, is one I like to call the personspace proximity theory of identity. There are X traits or attributes that a person has. Age. Sight. Hair Colour. Memories. Character. Intelligence. Etc… We consider some subset of these traits to be morally relevant to determining a person’s identity. Let’s call that set N. That gives us an N dimensional space in which a person is a point. Identity is that point. That is you. The further you move from that point, the less you that person is. Eventually you move far enough, let’s say into goldfish territory, and the difference is so great that you are no longer who you once were and in common speech we’d no longer call you the same person. This theory is nice because it avoids the problems of the physicalist and continualist theories. It’s also nice because it’s not discrete. Sudden cliffs or discontinuities in personhood are strange. Binary identities are weird. Moral reality is continuous, not discrete.