by Cuddy, Luke
In this thought experiment Hobbes wonders which ship would be Theseus’s ship, if not only were all the planks replaced, but if someone also collected all the old planks and put them back together into a ship. Then there would be two ships: one that has been called Theseus’s ship throughout its history and despite many repairs, and another which has been reconstructed from all of the discarded pieces of the original ship. So, which ship is Theseus’s ship, and why? If neither one is Theseus’s ship, what happened to it? If both are Theseus’s ship, how could there be two of them?
The paradox of Theseus’s Ship can be recreated in many forms. Consider, for example, Master Chief’s remarkable and iconic MJOLNIR armor. Imagine that a skirmish results in slight damage to a shoulder piece of Master Chief’s suit. After the battle, he gets the damaged piece replaced. One day while sprinting, some of the lift and speed of the suit lessens. More parts must be replaced. Eventually the helmet has taken so many blows that the faceplate cracks and the entire piece must be swapped out. Finally a processor inside the advanced exoskeleton suit has to be taken out and a new one installed. But it gets fixed and Master Chief dons his suit of armor once again.
Imagine that, gradually, every single bit of the suit gets worn out and replaced. Master Chief doesn’t even notice, but one day his MJOLNIR armor doesn’t actually contain a single piece of the same material that it started with. Is it the same suit of armor? Or is it a different one? If it is a different suit, when did it stop being Master Chief’s original suit of MJOLNIR armor and become a different one?
Now imagine that there is a technician responsible for making all of the repairs to Master Chief’s armor. When Master Chief returns from battle with some damage to the armor, he goes to see the technician, so that she can remove the damaged piece and install a replacement. But instead of junking the discarded piece of armor, the technician saves it and restores it in her spare time. At first, the technician just has a dented shoulder piece. Then she gets some conduits and crystal. One day Master Chief brings a cracked and battered helmet to her. Eventually, the technician is able to entirely recreate Master Chief’s suit of armor. Now there are two suits: which is Master Chief’s MJOLNIR armor? The one Master Chief is wearing, but which doesn’t have any of the original parts? Or the one in the technician’s possession, which was broken into fragments and then restored and reassembled? Is it neither? Is it both?
At heart this puzzle is about what makes something stay the same, and what makes it different. Another way the puzzle can be described is as presenting two conflicting criteria for identity: historical versus material continuity. Material continuity is pretty simple—it’s established via preservation of an object’s physical matter. So, an object has material continuity just as long as it is made of the same stuff. Historical continuity is a bit more complicated—it is established via an unbroken temporal trajectory. In other words, an object possesses historical continuity when it is possible, despite the various changes it may have experienced, to trace the object’s timeline in continuous stages from start to finish. Caterpillars and butterflies look like totally different creatures, but each butterfly was once a caterpillar, and it is possible to identify a particular butterfly as the same creature that was once a caterpillar by pointing to the unbroken timeline that leads from the caterpillar to the butterfly through a stage of metamorphosis. So, an object has historical continuity when it has an unbroken temporal trajectory, or a continuous history from one stage to the next.
In the case of the gradually repaired ship or suit of armor, there is clearly established historical continuity. Just as there’s an unbroken timeline during which the Athenians continue to refer to the ship as Theseus’s ship, despite many planks being taken out and replaced, so too there’s an unbroken timeline during which Master Chief continues to use his armor and think of it as his suit of armor, despite the many pieces taken out and replaced. But there is also the case of the reconstructed ship or suit of armor, which has material continuity. Hobbes’s imaginary second ship of Theseus is rebuilt from all the original planks, and thus is made of the same wood as Theseus’s original ship, just as the technicians second suit of armor is rebuilt from all the original pieces, and thus is made of exactly the same physical stuff as Master Chief’s original MJOLNIR armor.
Deciding which, if any, of the ships or suits of armor are the original ones depends on what seems more important to the determination of identity: historical or material continuity. If having an unbroken temporal trajectory as a certain object matters more than being made of the same stuff, then historical continuity determines sameness or identity. But if being made of the same physical material matters more, then material continuity dictates sameness or identity. Perhaps the best response to the puzzle is to consider both historical and material continuity when judging whether something is the same thing or different. But it is very difficult to construct a plausible and consistent solution to the general paradox that explains how to combine considerations of both historical and material continuity.
Making It Personal
The paradox of Theseus’s Ship as well as the corresponding example of Master Chief’s MJOLNIR armor are each about the identity of objects over time. These cases show that it is already a difficult matter to determine what makes a thing stay the same despite changes over time. Going beyond objects and talking about persons gets even more complicated, for several reasons. First, all persons are a kind of object, but not all objects are persons. To establish and maintain personhood must thus require something additional. Figuring out what that additional thing is and how to preserve its identity over time, despite changes, adds a new complication.
Second, neither historical nor material continuity seem like good criteria for the identity of persons over time. Persons lack strong material continuity. This is because most of the cells in our bodies are constantly replaced—so often, in fact, that less than ten years from now most of the cells in your body will not be the same as the ones there today.9 But you’ll still be you in ten years. This shows that material continuity must not be a very important criterion of personal identity: you won’t be made of the same stuff, but you’ll still be you.
Persons do often maintain a sort of historical continuity, but it’s not clear that this is required for the maintenance of personal identity. Imagine that there was a time traveler who jumped one hundred years into the future. She would no longer have a temporally continuous personal history, but her personal identity would still be the same. This simple thought experiment reveals that possession of an unbroken temporal trajectory is not required for a person to stay the same person. And consider Master Chief, cryogenically frozen at the end of Halo 3, drifting in space with Cortana, awaiting rescue. He has entered a sort of suspended animation, waiting for his life to start again when he is needed. But despite this break in his personal history, he’ll still be Master Chief when he wakes up. This shows that historical continuity must not be a very important criterion of personal identity: you can still be you even if there is a break in your personal timeline.
So, the identity of persons over time is complicated in a way beyond that of other objects, and requires criteria beyond that of material and historical continuity. The most obvious alternative candidate is known as psychological continuity. Psychological continuity refers to the continuity of various mental features deemed important to the preservation of personal identity. Relevant mental features might include memories, personality traits, emotional tendencies, and beliefs. When considering what makes persons unique and how they relate to themselves and other persons, it seems intuitively plausible that these sorts of mental features would be critical to the establishment and perseverance of a person’s identity.
This importance of mental features is famously expressed by the English physician and philosopher John Locke, who lived during the seventeenth century. In his Essay Concerning Human Understanding, a treatise on the human mind and self, Locke considered the hypothetical case of
a transfer of consciousness from one person to another. Locke wrote: For should the soul of a prince, carrying with it the consciousness of the prince’s past life, enter and inform the body of a cobbler, as soon as deserted by his own soul, every one sees he would be the same person with the prince, accountable only for the prince’s actions. (Section 15, Chapter 27)
This quote shows that, when imagining a person with the soul and consciousness of a prince in the body of a cobbler, Locke thinks that the identity of the person is determined by the intangible rather than the corporeal. In other words, consciousness determines the person, not the body their consciousness happens to be housed in. On this view, the prince-cobbler hybrid is really the prince trapped in the cobbler’s body, not the cobbler inconvenienced by the prince’s soul and consciousness. Additionally, Locke thinks that the idea being expressed here is not just his opinion, but a generally shared sentiment; that is what he implies when he claims that “every one sees” the case in the way he has presented it.
The ubiquity of Locke’s own viewpoint can be tested by posing other, related thought experiments. Consider the Flood, and the way in which this parasitic life form infects sentient beings. Once the Flood has infected a host organism, it begins a process of evolution through various stages. The host is gradually transformed from itself into some form of the Flood, such as a Carrier or Combat form. At some point the host organism has lost its original identity and become a member of the Flood instead.
Although the Flood exists within the body of the original organism, and there is an unbroken timeline from the organism through infection to the Flood form, once the original sentience is gone it seems incorrect to say that identity is preserved. Often Combat forms of the Flood inhabit the bodies of Covenant soldiers, but it would be strange to blame the original soldiers for the actions of their bodies once the Flood form has taken over. The identity of the organism has changed: although there was once a Covenant soldier there, that being is gone and now there is something else in its place, a different creature. Agreement with this assessment of the situation demonstrates agreement with Locke’s position: once psychological continuity has been lost, so too has personal identity.
A Psyche Connection
So, Locke’s thought experiment with the prince and the cobbler is simply an early statement of the common feeling that psychological continuity determines personal identity. Locke himself focused on memory as the mental feature responsible for generating psychological continuity. But there are problems with this way of looking at identity.
Less than one hundred years after Locke’s death, another philosopher named Thomas Reid offered a very powerful objection to Locke’s account. Locke’s view was that personal identity consists in consciousness alone, and that “whatever has the consciousness of present and past actions is the same person to whom they both belong” (Section 16, Chapter 27). This sounds relatively straightforward, but in his essay On Memory, the third of his Essays on the Intellectual Powers of Man, Reid posed the following scenario:Suppose a brave officer to have been flogged when a boy at school for robbing an orchard, to have taken a standard from the enemy in his first campaign, and to have been made a general in advanced life; suppose, also, which must be admitted to be possible, that, when he took the standard, he was conscious of his having been flogged at school, and that, when made a general, he was conscious of his taking the standard, but had absolutely lost the consciousness of his flogging. (Section 3, Chapter 3)
According to Locke, since the general remembers being the officer, the general is the same person as the officer, and since the officer remembers being the boy, the officer is also the same person as the boy. This logically implies that the general is the same person as the boy as well. But the fact that the general cannot remember being the boy means that, according to Locke, the general is not the same person as the boy. The general both is and is not the same person as the boy. Reid’s example shows how Locke’s view leads to contradiction, and is therefore illogical.
It is possible to reconstruct Reid’s example with Master Chief’s own history. Imagine John, a young boy just six years old, soon after his abduction from home and at the very beginning of UNSC’s SPARTAN-II program. The newly renamed John-117 probably remembers being John, the boy from Elysium City. But by the time he’s turned fourteen, he has undergone a rigorous training program, endured many physical and mental modifications, and is ready for his first mission. He might not remember being a normal boy as well as he did when the transformation had just begun. And after years of fighting as Master Chief, the supersoldier? He might not remember his life before becoming a Spartan at all. Imagine that Master Chief can remember training as John-117, and John-117 can remember being just John, but Master Chief can’t remember just being John. Memories can connect each of the stages of his life to the one before it, but they don’t reach all the way from the last to the first. This implies that Master Chief, the experienced supersoldier, both is and is not the young pre-abduction John. That’s a contradiction, and views that contain contradictions are usually considered to be fatally flawed.
Reid’s kind of case shows that relying on memory to establish psychological continuity is insufficient. But by taking various other mental features into account, perhaps it is possible to create a more robust account of psychological continuity. Recall that other potential candidates included personality traits, emotional tendencies, and beliefs. Combining these might be enough to generate an account of psychological continuity. But again, figuring out how to do that is tricky.
When defining things, philosophers often talk about necessary and sufficient conditions. Necessary conditions are the features that something must have in order to fit the definition of that thing. For example, a square is defined as a four-sided, two-dimensional, closed figure. Having four sides is a necessary condition of being a square. If a figure does not have four sides, it cannot be a square. But just having four sides does not make something a square. A pyramid with a triangular base has four sides, for example, but it is not a square. This is because having four sides is a necessary, but not a sufficient, condition for being a square. A sufficient condition is a feature that makes something qualify as the thing it is defined as. For example, being a square is sufficient for being a closed figure. If a figure is a square, then it must be a closed figure. But something does not have to be a square to be a closed figure. It could be a triangle instead. This is because being a square is a sufficient, but not a necessary, condition for being a closed figure.
This conception of necessary and sufficient conditions can be used to help evaluate the preceding discussion of personal identity. The constant replacement of bodily cells shows that, even under normal conditions, material continuity is not necessary for the preservation of personal identity. Locke’s case of the prince and the cobbler shows that material continuity is not sufficient. The possibility of time travel shows that historical continuity, although usually a component of personal identity, is not necessary for the preservation of personal identity. And the transformation of sentient beings into Flood forms shows that historical continuity is not sufficient. But psychological continuity does seem necessary for the preservation of personal identity. Perhaps among the various mental features which make up psychological continuity, such as memory, personality, emotion, and belief, no single one by itself is necessary, but together they are sufficient.
Mastering the Chief
Establishing the identity of objects and persons over time is surprisingly difficult, as this discussion has shown, using a mix of cases from both the real world and from the fictional world of Halo. Notable examples from the history of philosophy, as well as the traditional philosophical method of constructing thought experiments, have been applied too. But there are some additional aspects of the particular identity of Master Chief that are worth further consideration. These are his status as a fictional character, his lack of a discernable face, and the fact that he has been cloned.
This has two important implications here: first, there’s generally only one version of each real person, but there can be infinitely many versions of a fictional character. Philosophers like to make a distinction between types and tokens. Types describe a kind of thing, whereas tokens are instantiations of type. AIs are a type of thing, and each AI, such as Cortana, is a token of the type AI. Real persons are also a type of thing, and each of us are tokens of that type. Actually, each of us is also our own particular type of thing—but there’s just one token of that type. The type that describes me, Joyce C. Havstad, only has one token of the type—there’s just one version, a single instantiation, of me. This is not the case for fictional characters like Master Chief. The type that describes Master Chief has many tokens in it: in code, on disc, in novels, on screens, and in minds. There is a plasticity about fictional characters that allows for mass instantiation and creatively different versions—for many tokens to exist within the type. Real persons like you and me do not have this kind of plasticity, but fictional characters like Master Chief do.
Second, real persons are physical objects located in space and time, whereas fictional characters are mental constructs produced by imagination and narrative. Instead of being constructed and influenced by an assortment of material, biological, psychological, social, and historical factors, Master Chief’s personal identity is determined by a group of story and game creators at Bungie. It is also, to some extent, determined by each player of Halo. This is an ingenious consequence of generating a character without a face. By never revealing, and perhaps never even creating, the face of Master Chief, the designers of the game allow each player to imagine Master Chief’s face however they choose. Part of his personal identity is unfixed, and can thus be envisioned in a multitude of ways. Players can make up and relate to the character that they choose, enhancing the bond between player and character.