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.

Causation and memory theories of personal identity

Unlike soul-based theories, the memory, brain and body theories of personal identity are subject to fusion cases. There are four options as to what happens when persons merge:

• Singleton: a specific person continues, but we don’t know which one

• Double Identity: there was only one person prior to the fusion, wholly present in two places at once

• Scattered: there was only one person prior to the fusion, half of whom was present in one location and half of whom was present in another

• End: fusion causes the person’s demise and the arising of a new person.

The problem with Singleton is that it supposes there is a fact about personal identity deeper than facts about memories, brain-continuity and body-continuity, which undercuts the motivation for the three theories of personal identity.

Double Identity and Scattered are weird. Moreover, it leads to absurdity. For whether you and I are now one person or two depends on whether we will in fact fuse in the future, and we have backwards counterfactuals like: “If you and I fuse, then we will have always been one person.” This is just wrong: facts about your being a different person from me should not depend on what will happen. And consider that if you and I decide to fuse, thereby ensuring that we have always been one person J, either bilocated or scattered, then J exists because of J’s decision to fuse. But an individual cannot exist because of a decision made by that very individual.

That leaves End. I think End may be a good move for brain and body theorists. But it’s not a good move for memory theorists. For by analogy, we will have to say that fission causes a person’s demise, too. But then it is possible to kill a person without any causal interaction. For suppose you are unconscious and undergoing brain surgery under Dr. Kowalska. Dr. Kowalska scans your brain to a hard drive as a backup. A malefactor steals the hard drive from her as well as a blank lab-grown brain. If the thief restores the data from the hard drive into the lab-grown brain, that will result in fission and thus death. But the thief’s restoring of the data into the blank brain is something that can happen without any causal interaction with you. Hence, the thief can kill you without causally interacting with you, which is absurd.

Hence both Double Identity and End have causality problems on the memory theory: Double Identity allows someone to be literally self-made and End allows for killing without causation. It may be that if one is less of a realist about causation, these problems are less, but since memory itself is a causal process, it may be that memory theories of personal identity don’t sit well with being less of a realist about causation.

Why my present existence can't depend on future events

I find very persuasive arguments like this:

1. If theory T is true, then whether I exist now depends on some future events.

2. Facts about what exists now do not depend on future events.

3. So, theory T is not true.

For instance, some four-dimensionalist solutions to problems of fission according to which the number of people there are now depends on whether fission will are subject to this criticism.

But I’ve had a nagging worry about arguments like this, that in accepting (2), I am not being faithful to my eternalist four-dimensionalist convictions: why should the present aspects of the four-dimensional me have this sort of priority? Moreover, I didn’t really have an argument for (2). Until today.

Here is an argument for (2). Start with this.

4. If facts about my present existence depend on future events, then facts about my present existence depend on future events that happen to me.

For instance, suppose that whether I exist now depends on whether some surgeon cuts my brain in half tomorrow. Well, then, some of the events that my present existence depends on will be events that happen entirely to someone else—for instance, whether the surgeon gets to work on time. But other events, such as the cutting or non-cutting of the brain, will happen to me. It would be absurd to think that facts about my present existence or identity depend on future events that happen entirely to something other than me.

Then add:

5. Any events that happen to me in the future depend on my present existence.

For, such events presuppose my future existence, and my future existence is caused by my present existence.

6. Circular dependence is impossible.

7. So, facts about my present existence do not depend on future events.

Note that (6) is a very strong premise, and is one place the argument can get attacked. Many people think that you can have circular dependence when the dependence in the two directions is of a different sort. In the case at hand, facts about my present existence might depend constitutively on future events, while the future events depend causally on my present existence. Nonetheless, I think (6) is true, even if the dependence in the two directions is of a different sort.

Another move is to describe the future events on which my existence depends without reference to me. Don’t describe what the surgeon does as the splitting of my brain, but as the splitting of brain x. Then we could say that the future event of the surgeon’s splitting my brain does depend on my present existence, but my present existence doesn’t depend on that event. Instead, it depends on the future event of the surgeon’s splitting brain x. This objection denies (5): while the splitting of my brain depends on my present existence, the splitting of brain x does not, and yet it happens to me.

I think this is mistaken. The splitting of brain x depends on the future existence of that brain, and that brain depends on me, because parts depend on wholes—that is a deep Aristotelian premise I accept. Thus I think (5) is true. An event that happens to me is an event that involves at least a part of me, and none of my parts could exist without me. Granted, a brain like mine could exist without me. But token events are individuated in part by the things caught up in them. A splitting of a brain merely like mine would be a different event from the splitting of this particular brain. And it is a token event that my present existence is supposed to depend on.

The above argument won’t move non-Aristotelians who think that wholes depend on parts rather than parts depending on wholes. But it works for me. And hence it assuages the worry that in accepting (2), I am being unfaithful to my views about time.

All that said, I don’t really want to affirm (2) in an exceptionless way. If I am a time-traveller born in the year 2200, then my present existence does depend on what will happen in the future. But it only depends on what will happen in the external-time future not on what will happen in my internal-time future. And, crucially, I think time-travel is only possible when it doesn’t result in causal loops. So even if I am a time-traveller from the future, I cannot affect anything that is causally relevant to whether I will be born, etc. This probably means that if time-travel is possible, it is possible only in very carefully limited settings.

Fission and making the world have been a happier place

One theory about what happens in cases of personal fission is this. If a person is split, then there were two colocated people there all along. This fits best with four-dimensionalism. There are, in cases of fission, two people who overlap for a part of their four-dimensional career.

Here is a curious consequence. Suppose that Jim has led a very happy life. Then if I were to split him, I would bring it about that there have always been two happy colocated people there. But increasing the number of happy people makes the world a happier place. So, were I to split Jim, I would make the world have been a happier place. Surely, though, we don't have the power to make the world have been a happier place. So we should reject this four-dimensionalist solution to the problem of fission.

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.

Essential properties and self-dependence

My being seated now is causally explained by my having sat down. Suppose that my being seated now is an essential property of me. Then, had I not sat down, I wouldn't have existed. So my very existence would have counterfactually depended on my own causal activity. But that would absurdly make me be something too much like a causa sui.

This seems to generalize into an argument for a general principle:

1. No property that counterfactually depends on an entity's own non-essential causal activity can be essential to that entity.

I needed to specify that the relevant causal activity is non-essential, because there is nothing deeply absurd about an entity that has some essential properties follow from causal activity that's essential to the entity.

But the form of argument that I used to get to (1) gives other results. For instance, a leading theory of personal identity holds that in cases where symmetric fission occurs—apparently, a person splitting into two—there were already two co-located people there before the fission. But why are there two people there? Presumably precisely because fissioning occurred—otherwise, there would have been only one.[note 1] Thus the existence of the two people is explained by the fission. But surely if fission is possible, it's possible that it be triggered by the non-essential action of the fissioning individual or individuals. In that case, then, the existence of the two people is explained in part by their very own activity. So this account of fission leads to something like self-dependence and should be rejected.

There may, however, be an objection to the argument. Suppose that the causal self-dependence is not fundamental. Instead, more fundamentally, we have a case where the whole depends on the contingent causal activity of a part. For instance, we may think that the length of an event is an essential property of an event. But the length of an event frequently depends on the contingent causal activity of a part of the event. (Thus, the length of World War II depends on the effects of D-Day, even though D-Day is a part of World War II.) In some such cases we might say that the whole depends on its own causal activity, since the causal activity of the part can sometimes be attributed to the whole.

I am not convinced. I think that in cases like this, it is incorrect to say that the whole depends on the whole's causal activity, but that it depends on the part's causal activity, and in this case the part's causal activity is not in fact correctly attributed to the whole.

In any case, the part-based objection will only apply in cases where the whole's causal activity is derivative from the part's causal activity. I think free choices are not derivative from the causal activity of anything other than the person as a whole, so in the fission case it's still impossible that whether there are two persons should depend on their choices. But this is rather controversial.

If there are cases where the whole depends on its own causal activity because its causal activity is derivative from a part's causal activity, then (1) needs to be qualified to apply to fundamental entities.

Punishment, time, and a poor objection to identity after fission

It is a truism that the punishment should follow the crime. Thus, even if you know with enough certainty for court conviction that Smith will commit a crime, that is not enough for punishment.

But we need a qualifier. Punishment only needs to follow the crime in internal time. Smith builds a time machine while in prison and travels to 160 million BC. Now, there is a small police outpost in 160M BC, protecting time-traveling scientists from nefarious time travelers, and there is a small jail. It turns out that backwards time travel is much cheaper than forwards time travel (at any decent speed, measured in the ratio of external to internal time). To send Smith back to his time would be prohibitively expensive. There would be no injustice in jailing him in the year 160M BC, notwithstanding his protestations that he hasn't committed any crimes yet. For that's only true according to external time, since by his internal past, he had committed crimes.

Now, consider an apparent case of a person fissioning, say due to a Star Trek transporter malfunction. I used to argue that it is not tenable to suppose that the result of that is a single bilocated person on the grounds that it would be then be appropriate to punish the person in one location for what their copy in the other location did, which seems absurd. But I now think this argument is mistaken. For on the hypothesis that the person comes to be bilocated, we should now think of the person's internal time as having different branches corresponding to each location (this can best be seen by noting that we can run twin paradoxes between them). But then it is false that the person in location A can be justly punished at t₂ for what the person in location B had done at an earlier time t₁. For punishment should follow the crime in internal time. But since the two internal timelines are parallel, what B did is neither earlier than, nor simultaneous with, nor later than the punishment of A—there is no comparison between these internal times. Of course the external time of the punishment is later than the external time of the crime, but that is irrelevant. If parents took a 14-year-old Hitler for a time-travel excursion to our time, it would be wrong for us to now punish the young Hitler for the crime he had committed in the 1930s, since those crimes would not be earlier than the punishment in his internal time.

So while there might be objections to identity-after-fission, the punishment objection is not very strong.

One qualifier: It would not be wrong to set things up so that the punishment would be simultaneous with the crime, as long as the crime caused the punishment in the right way. So where I say that the punishment should follow the crime, I should include the possibility that the two are internally simultaneous, but with the crime explanatorily prior.

Memory theory, fission and faster-than-light influences

Standard memory theories of personal identity says that what is necessary and sufficient for identity is a chain of memories (or, more precisely, quasi-memories) and the absence of fission or fusion of memories. Now suppose:

1. If we keep fixed the laws of nature and miracles don't happen, then what is done five light years from earth at t cannot affect whether I am on earth five minutes after t (keeping a constant reference frame throughout).

Suppose physicalism is true. Then it is in principle possible to perform the following operation: record the state of my memories, freeze me, and send the records to a location five light years from earth. At that location the records can be downloaded into a fresh brain. So, suppose my memories have been recorded, I'm frozen, and the records are five light years from earth, where, at time t, someone is deciding whether or not to download those records into a fresh brain. At the same time (in this frame), I am being thawed. If they download the records into a fresh brain, then at t I will experience fission, and cease to exist according to standard memory theories. But that violates (1): whether they download the records into a fresh brain affects whether I am on earth five minutes after t.

One can get out of this problem, at the cost of other weirdness, by allowing one to survive fission. Another way is to deny physicalism—without physicalism it is not clear that memories can be transfered, as they may not be entirely brain-based.

But one might also try for the following solution. Suppose they do download the memories into a fresh brain. Fission doesn't count as occurring then. After all, reference frames are arbitrary, and so such a "then" would be arbitrary. Fission only counts as occurring when one of my memory-continuants is in the forward light-cone of another of my memory-continuants. And that will happen five years after the operation, and hence will not violate anything like (1). I don't know how attractive this view about fission is. It would be weird to build into a memory view something so tied to the physics of our world. One would need to say something about how the memory view changes in worlds with different physics. I still think a better move is just to deny the memory theory. But this interesting move would be worth thinking about.