Most religions believe that we have a soul. They don’t quite define what it is, but they are all quite sure that we have it.
A bit of reading in philosophy will lead us to the notion that the soul holds the key to our personal identity. In other words, if I put your soul in my body, then you would find yourself trapped in my body. My body would not be going around feeling that there is a strange something inside me. So your soul is expected to be the key to your personal identity.
Now, let’s take that thought experiment a bit further. Let’s say your soul and mine are swapped so that you should find yourself in a strange body. But then, along with that, let’s say our memories, beliefs and hopes are also swapped (through some clever brain dump and uploading, for instance), which means your soul in my body has all my memories, intentions, opinions etc., and none of yours. Would you feel as though you are in a wrong body? Probably not, because you are operating with my memories, beliefs and so on. So you would believe that you are in the right body.
Thinking along this line, we would find it normal to consider the totality of our beliefs, intentions, memory etc. as the key to our personal identity. Still skeptical about this argument? If so, consider another situation in which our brains are physically swapped. Would you then feel as though you are in a wrong body? I would think so, because you brain contains all the information about who you are and what your body should be. Logically, there shouldn’t be any difference between swapping the brains physically, or uploading and rewiring the brain.
Even when we logically accept the argument about the key to personal identity being all the software in the brain, we still do not quite buy it. And I know why. Secretly, we all believe that there is an internal locus of personal identity and an external one. For instance, even after uploading your brain contents into mine, if you prick my finger (the finger of my original body, to be very precise), the entity that would feel the pain would be me, not you – or so you might think. It is this feeler, this entity, that I call the internal locus of personality, and most people call the soul.
This notion of an internal locus, a feeler, or a soul is false, however hard it is to come to terms with it. If you read Zen and the Art of Motorcycle Maintenance, and ponder over the personality that was annihilated by electroshock therapy, you will have to accept that it is the state of the brain, the software running on it, that determines the personality. If you still hold on to the soul being the key to personal identity, you would have to come up with a convoluted story where one soul (that of Phaedrus) was tucked away somewhere (since souls don’t die), another one (that of Richard Pirsig) was instilled for a while, and later on, both of them were in the same body!
So, it looks to me that the totality of our thoughts, memories, beliefs, goals, hopes etc. is the key to our personal identity. The totally, of course, goes by the name of consciousness. Even though it gives us the illusion of selfhood, and an illusion of an internal locus of personal identity, that part is merely incidental, epiphenomenal.
What I did through the thought experiments above is to push the agenda of physicalism. I kind of proved that the key to personal identity is in fact the three pounds of grey matter that we carry around in our head, and the neuronal connections and electrical patterns within. There is nothing else. Nothing.