Alicia clearly remembers visiting the Parthenon in Athens, and how the sight of the crumbling ruin up close was less impressive than the view of it from a distance, perched majestically on the Acropolis. But Alicia had never been to Athens, so what she remembers is visiting the Parthenon, but not her visiting the Parthenon.
It is not that Alicia is deluded. What she remembers is actually how it was. She has had a memory implant. Her friend Mayte had been to Greece for a holiday, and when she came back she went to the Kadok memory processing shop to have her holiday recollections downloaded to a disc. Alicia had later taken this disc back to the same shop and had the memory uploaded to her brain. She now has a whole set of Mayte's holiday memories, which to her have the character of all her other memories: they are all recollections from the first person point of view.
The slightly disturbing thing, however, is that Mayte and Alicia have exchanged such memories so many times that it seems they have quite literally inhabited the same past. Although Alicia knows she should really say that she remembers Mayte's holiday to Greece, it feels more natural simply to say she remembers the holiday. But how can you remember what you never did?
Source: Section 80 of Reasons and Persons by Derek Parfit (Oxford University Press, 1984).
Baggini, J., The Pig That Wants to Be Eaten, 2005, p. 88.
This is now the second thought experiment inspired by Derek Parfit, who has been highly influential among contemporary philosophers on the subject of personal identity. Parfit is a reductionist, "believing that since there is no adequate criterion of personal identity, people do not exist apart from their components." In a late 1990's documentary on Channel 4 called Brainspotting, Parfit described four traditional theories of what components might constitute the self: the body, the brain, memories, or a soul. (You can see Parfit discuss this in two 10-minute clips here: Part 1, Part 2.) As an evolutionary philosopher looking at the evidence in nature, I've already dispatched with the idea of the soul. Descartes' dualism was thrown out long ago too, so we can rule out the body or the brain as separate entities that are able to work one without the other. And in the first Parfit-inspired thought experiment on the teletransporter, we saw that memories alone are also not able to necessarily and sufficiently explain personal identity. For example, what if the teletransporter made three of you that all remembered the same things? It's obvious that the three of you would diverge quickly into independent beings, but even before the divergence happened, there wouldn't only be one of you after the other physical copies had been made.
So if none of the four traditional components tell the story of identity, what are we left with? The way Parfit explains it in Brainspotting, he sees personal identity rather like David Hume saw the definition of a nation. A nation is generally considered to be a group of people living on a portion of land, but it's not just "those people" nor just "that land". However, it's also not something over and above that either—the nation is not some permanent immaterial entity, it's just an ever-changing definition. To Parfit, the individual self can be regarded the same way. It is the totality of a set of perceptions within a body (which includes a brain); it is not just the body or just the perceptions. Problems arise when we mistakenly try to insist on one permanent definition of a single self. We are beings who change over time and our identities do as well.
I'm very sympathetic to these arguments, as I explained in my Response to Thought Experiment 11: The Ship Theseus, when I said:
The universe and everything in it are always changing in almost infinitesimally continuous ways. We've developed the branch of mathematics called calculus to help describe these tiny changes, but it would be incredibly difficult to keep track of reality this way by calling everything x, then x1, then x2, then x3, etc. on into infinity. It's much easier for our brains and our languages to just call something X and treat this x as a concrete thing even though it actually has very fuzzy borders at the edges.
So when Alicia and Mayte exchange memories (assuming that is possible), they aren't slowly becoming one person, they are just each changing slightly to be bodies with some shared perceptions. In my post on John Locke (whose theory of mind is often cited as the origin of modern conceptions of identity and the self), I gave another analogy for this that might be helpful:
Identity lies at the Mind x Body intersection. One helpful analogy is to say identity is like a river. Not the water that flows through it, but the channel that actually forms the river. When storms occur and water is high, the river is deepened. When drought occurs, the river slows and silts up. When earthquakes or glaciers reshape the landscape, the riverbed may hold no water at all. If we know the events that carved the river, we can recognize its identity no matter what state it is in. Likewise, we can recognize identity when we know the events that shaped it. If you know the river and are told the volume of water that will flow its way, you know what the river will look like. If you know a person and are told the events that will occur to them, you will recognize how they handle it. This is how we know people after long absences, and this is how changes during brief separations can surprise us.
These questions of personal identity are the major points of discussion intended by this thought experiment, but what of the final parting question that Baggini throws in: "how can you remember what you never did?" I have serious doubts that we will ever be able to download and upload synaptic connections such that all the sense connections attached to one memory in one specific body with a very particular set of sense organs, could ever be replicated in a convincing manner in another brain composed of connections formed from sensory impressions using another set of sense organs, but if we ever figured that all out, then sure, we could "remember what we never did." In fact, as long as the upload process got close enough, as we recalled the uploaded events over and over and rebuilt and altered the connections surrounding those events, the memory would become our own. This already happens all the time with false implanted memories. But then again, in the context of this thought experiment, then Alice and Mayte would no longer keep rebuilding their memories in the same way and they would start to diverge, once again separating their personal identities. And thus the river would flow on...