Partial amnesia and fission

Some cases of partial amnesia present a prima facie problem for memory theories of personal identity (the theorist will bite the bullet on total amnesia, of course). At 9 pm, Bob starts to drink. At 11 pm, he makes a fool of himself. At midnight, he passes out. At 9 am, he wakes up remembering nothing that happened after 10 pm. Obviously, at 9 am, it’s the same person as the one who made a fool of himself the night before, but there is no chain of memories from the 9 am self to the 10 pm self.

There is a simple solution: don’t talk about chains of memories, but instead talk of chains of memory-links. Memories are unidirectional (you remember later what happened earlier) but memory-links are bidirectional: when at t₂ you remember what happened at t₁, there is a memory link from t₁ to t₂ as well as from t₂ to t₁. And now we have a chain of memory links: the morning-after self is memory linked to the 9 pm night-before self, and the 9 pm night-before self is linked to the 11 pm night-before self (Bob at 11 pm remembers starting to drink at 9 pm). So the morning-after self is the same as the 11 pm night-before self, much as he might wish he weren’t.

But here is an interesting thing. If we think about this scenario, formally this is a case of fission. There are two memory branches:

1. starting at 9 pm, then going on to 10 pm, 11 pm, and up to midnight, and then fizzling out forever

2. starting at 9 pm, then going on for a little bit, then skipping until 9 am.

So, partial amnesia cases like the above are actually cases of fission. And in cases of fission, most people do not want to say that we have the same person in the two branches. The most popular solution is that fission is death, and a second option is a four-dimensionalist one on which the occurrence of fission shows that there were two people there all along. But neither option is plausible for our partial amnesia case. It is absurd to say that Bob automatically dies around between 9 and 11 pm. And it is absurd to say that there used to be two people in Bob’s body all along. Those are extreme solutions that might fit science-fictional cases, but surely are not appropriate for all-too-common cases like Bob’s.

Perhaps we can say this: real fission requires there to be two simultaneous branches. So now our theory is this:

3. when memories branch, and the two branches are simultaneous, then something metaphysically weird happens (either there were two people before the branching or the pre-branching person has died).

But (3) fails in time-travel cases. Suppose Bob owns a time-machine. At 9 pm, Bob goes into a time-machine set for midnight. He keeps on drinking in the machine for two more hours, until 2 am. Then he passes out and loses the memory of the last two hours of drinking while the time-machines auto-pilot pulls him back to midnight and dumps him in his bed. We now have two branches starting at midnight: Bob drinking in the time-machine for two hours and Bob sleeping in bed with loss of memory of two hours of drinking. But it seems wrong to say that by adding a time-machine to the original partial-amnesia story, thereby making the two branches simultaneous, we would get the weirdness of having Bob perish or having always had two persons there.

Suppose you think backwards time-travel is impossible because of the paradoxes that result. You should still think of forwards time-travel as possible. Indeed, non-instaneous forwards time-travel is possible: that’s what happens in the twin paradox from relativity theory. But there is nothing logically absurd about instantaneous forwards time-travel. But any case of simultaneous-branch fission can be transformed into a case of non-simultaneous-branch fission by forward traveling one branch right after branching to a future time after the other branch has perished. Thus, we really shouldn’t treat simultaneous and non-simultaneous branchings differently.

I think this is a serious problem for memory theories of personal identity.

Personal identity, memory and fission

Suppose that (a) memory connections are constitutive of personal identity and (b) fission of memories destroys a person. If one accepts (a), then (b) is very plausible, so (a) is the crucial assumption.

Now consider this case:

• At 4 pm, due to trauma, Sam suffers complete and irreversible amnesia with respect to events between 2 pm and 4 pm.

Then the 5 pm Sam has first-person memories of the 1 pm Sam, and it seems thus that:

1. The 5 pm Sam is identical with the 1 pm Sam.

But the 3 pm Sam also has first-person memories of the 1 pm Sam, and by the same token:

2. The 3 pm Sam is identical with the 1 pm Sam.

By symmetry and transitivity:

3. The 3 pm Sam is identical with the 5 pm Sam.

There is as yet no absurdity here. There is, after all, a chain of memory connections between the 3 pm Sam and the 5 pm Sam, though the connections don't run in the same direction (3 pm Sam remembers 1 pm Sam who is remembered by 5 pm Sam). But I think there is a tension between (3) and (b), the claim about fission. For now imagine a different case:

• At 2 pm, Sam's memories are copied into a spare brain, call it Bissam, and Bissam immediately time travels forward to 4 pm. (Forward time travel does not seem metaphysically problematic.) At 4 pm, Sam is killed.

This is clearly a case of fission, and so the 1 pm Sam no longer exists at 5 pm. But in terms of the structure of memories, this case is exactly the same as the initial amnesia case. The 5 pm Bissam remembers (or quasi-remembers, if we want to nitpick) the 1 pm Sam but not the 3 pm Sam. Likewise, in the original story, the 5 pm Sam remembers the 1 pm Sam but not the 3 pm Sam. In both stories the 3 pm Sam remembers the 1 pm Sam. So it seems that in both cases the 5 pm person and the 3 pm person are the results of the fission of the pre-2 pm person. Well, almost. Bissam exists for an instant at 2 pm while the memories are copied into him. But that isn't essential. We could imagine the copying process works such that the memories are only fully seated once Bissam arrives at 4 pm.

So the memory theorist who thinks that fission kills a person should think that total amnesia with respect to a short time period also kills one.

But if that's right, then we don't survive those nights where we do not remember our dreams upon waking up. For the dreaming person has memories (skill memories at least; but also temporarily inaccessible episodic memories) of the person who went to bed. But the waking person doesn't have memories of the dreaming person, though she does have memories of the person who went to bed. So the person who went to bed fissions into the person who dreams and the person who wakes up.

This means that the memory theorist shouldn't think that fission kills. (Another standard argument for this conclusion: If fission kills and identity is constituted by memory, then you can be killed by having your brain scanned and the data put into another brain; but you can't be killed by a process that doesn't affect your body.) But if fission doesn't kill, then it seems that the best view is that in cases of fission there have always been two persons. And that leads to various absurdities, too.

Psychological connectedness/continuity and self-sacrifice

At least if I have no dependents, it would be praiseworthy, supererogatory and hence permissible to sacrifice my life to save the life of a stranger. It is permissible to take actions to save a stranger's life that I foresee (but do not intend) will cause my immediate death, and I equally have the right to take actions to save a stranger's life that will result in my dying in 20 years (e.g., because to save the stranger's life I need to brave some radiation hazard which will eventually kill me.

This is true even if I foresee that my character will shift in significant ways over the next 20 years, that I will then not have many memories of how things are for me now, and so on. In other words, I have the right to sacrifice the life of my future self for a stranger even if my future self will not be very much psychologically connected to me. On the other hand, I have no right to sacrifice the life of my friend for a stranger without my friend's permission, and the closer the friend is to me, the worse such a sacrifice would be. This shows that my relationship to my future selves is significantly unlike my relationship to my friends. It does not matter how psychologically close to or distant from my future self I am--I have the right to make the sacrifice. But the closer I am to my friend, the worse it is to sacrifice the friend for a stranger without the friend's permission.

Thus, sometimes, identity matters, and psychological connectedness is largely irrelevant. Could one replace identity with psychological continuity in these considerations? No. For suppose that I know that next week I will fission into two individuals. I will have psychological connectedness and continuity with them. But I have no right to sacrifice their lives to save the lives of two strangers, e.g., by exposing myself now to a dose of radiation that will result in the two descendant individuals dying in two weeks. It would be like sacrificing the lives of two children of one's own to save two strangers. The psychological connectedness and continuity are insufficient for permissibility here. And even if it were permissible, it would hardly be praiseworthy.

Or consider the following scenario. Rescuing the stranger will result in a dose of a substance to oneself that will first induce amnesia and then death. On psychological continuity theories, the person who dies is the person who inhabits your body after the amnesia and this is not you because of lack of psychological continuity (one might add that one has no plans for this person if need be). And so you have sacrificed the lives of two people to save the stranger--for you will die through the amnesia (on psychological continuity theories, amnesia is a cessation of existence), and then the new person who will come to exist in your body will die. So this is imprudent (sacrificing two to save one) and immoral (one of the sacrificed has not been consulted). But that is absurd--surely it makes no difference whether the substance directly causes death, or causes amnesia followed by death.

(In fact, the latter consideration seems a nice independent argument against psychological theories. Suppose that you're dying. Treatment A will give you 100 days of life. Treatment B is slightly less painful, and will result in 100 days of life, followed by amnesia, followed by an hour of life, followed by death. It seems permissible to opt for Treatment B. But if Treatment B means two people die--one through amnesia and another after--it may not be permissible to opt for it just because it is slightly less painful.)