In her alien-invasion-plus-vampire novel THE MADNESS SEASON, C. S. Friedman creates a species called the Marra, incorporeal beings who wear material bodies "like clothes." Upon assuming a new body, a Marra constructs an identity to shape its lifetime in that persona. Being true to the present identity is vital to a Marra. For instance, the female-gendered Marra with whom the novel's protagonist becomes intimate currently lives as a healer. Yet through all the shifts of bodies and identities, each individual Marra remains the same person with continuity of memories. How can a self persist with no permanent physical form to anchor it, however? The Marra must be the SF equivalent of disembodied souls. Maybe the soul or self of a Marra is an energy network?
Of course, many religions believe in disembodied souls. The concept of reincarnation depends on the existence of a nonmaterial soul that moves from body to body through death and rebirth. As I understand it, the general belief holds that in a new life the soul doesn't remember past lives, so in what sense is it the same person? In folklore, fantasy, and horror, many tropes exist that conceive of the spirit as detachable, so to speak. Ghosts can linger on after the death of the body. In stories as different as FREAKY FRIDAY and Lovecraft's "The Thing on the Doorstep," people can trade minds between bodies by magic.
On the physical level, cells in our bodies are constantly wearing out and being replaced. Different tissues get replaced at different rates. So if we don't have the same body we had at birth, are we the same person or a different person sharing some memories with the earlier one? Accepting the second answer would have scary implications, because it could mean that someone suffering from severe dementia-related memory loss is no longer the same person despite bearing the same name. On the other hand, it's believed that neurons in the brain never get replaced, so does their existence provide continuity of selfhood?
In time-travel stories that allow two or more versions of the same person to exist in one moment of time, which is the "real" person? Both/all of them? If "selfhood" is defined by self-awareness, the status of existing in two bodies at once, each with its own separate awareness, generates a tangle of philosophical problems. Maybe selfhood follows the traveler's consciousness as it moves through his or her personal timeline; when you meet your earlier or later self, that's not a "real" self because your awareness isn't currently resident in that body. (So what does that make the earlier or later version? Some kind of zombie?) Dr. McCoy speculates in an early STAR TREK novel that the transporter doesn't literally project a person across space. Instead, the transporter destroys the individual at the origination point and creates a duplicate at the destination. Therefore, everybody who travels by transporter "dies" on the first trip, and every subsequent trip kills a version of that person and constructs a new version. Along the same lines, if you have your consciousness uploaded to a computer, and your body dies soon afterward, is the computer consciousness really yourself or only a simulation?
Some psychologists maintain that no such phenomenon as the unified self, the ego, exists. What we think of as the mind is a collection of different processes. Consciousness, according to these scientists, is an illusion the brain has created for its own convenience. The trouble with this hypothesis, in my view, is that the construction of an illusion of selfhood implies an agent to do the constructing. Therefore, we come back to a unified, controlling self.
Margaret L. CarterCarter's Crypt