Systems Thinking and Theseus' Ship

How can systems thinking resolve the paradox of the Ship of Theseus?

If we replace each component of a ship, one by one, until all components have eventually been replaced, is it still the same vessel?

The paradox is not merely about mythological ships, but about every living organism. In humans, all cells regenerate over time: skin cells regenerate every few weeks and skeletal muscles every decade or so. Are you the same person from, say, twenty years ago? Your identity card surely thinks so. But not a single cell from twenty years ago is still inside of you. Perhaps you have even changed physiologically.

Common solutions

I shall briefly highlight a few common resolutions before I present the view from systems thinking.

Heraclitus

Heraclitus thought that both the ship—and you or me for that matter—are not the same as time passes by:

No man ever steps in the same river twice, for it is not the same river and he is not the same man.

There you have it. The government is clearly wrong. Tear up your ID card!

Of course, the problem with this argument is that if all the properties of an object or entity must remain identical over time for an identity to persist, then an electron that flips its spin already has a new identity. Electrons are indistinguishable, so maybe that is not such a big deal after all.

Deflationism

Or maybe the problem lies in the labels we assign to things. If electrons had names like Kevin and Sally, maybe they would wonder about the Quantum Fields of Theseus. The deflationist view is that the problem merely lies in the meaning of labels, such as ‘ship’, ‘human’, or ‘electron’, not in the facts of the thought experiment.

Endurantism

Such diddling with semantics is also found in continuity identity theory, which is also known as endurantism. It posits that an object’s identity remains intact as long as it continuously and metaphysically exists under that identity. There needs to be a continuous connection throughout the evolution of an entity.

As long as the ship and you are replaced one plank of rotten wood or one cell at a time, their identities remain the same. And if you were to change everything of an entity at once, then there is no such a connection, and therefore the identity ceases to endure.

But what does ‘all at once’ mean? You cannot physically change all components of a ship instantaneously. Even if it happens in a few minutes or hours, it is still not instantaneous.

What is more, the identity of any adult is the result of continuous change from a zygote into a fetus, then a child, and finally an adult. A baby is, however, not an all-at-once entity that did not exist prior to birth, but rather a continuously developing entity within the mother. As such, it is hard to argue in endurantism for a separate identity for the child. Clearly, that is bonkers.

Perdurantism

Perdurantism is similar, though it uses more science-y language. It states that an entity is really not the three-dimensional thing in front of us, but it extends through time from the past into the future. It has spatial and temporal parts. It is therefore, really a four-dimensional entity, whose identity encompasses all time slices from the past into the future. You right now are just one slice of ‘all of you’.

In endurantism, all entities are three-dimensional and have no temporal parts: they exist only in the eternal now. It is their identity that remains, despite continuous change. You right now are all there is. If you think endurantism and perdurantism seem like a distinction without a difference, you are not alone.

The question with perdurantism is whether the time before construction/birth and after disassembly/death are part of the four-dimensional timeline of each object. If yes, then everyone’s and everything’s identity is linked to the blob of quantum fluctuations that started the universe with a big bang. This is roughly what eternalists argue. If not, however, then who decides what parts of the timeline are really part of the identity? It all feels a bit arbitrary.

Aristotle

Aristotle’s idea of causes can explain the paradox away. The physical object ‘ship’ can change but its formal cause (design) and its end cause (purpose) do not. That said, many ships share the same design and obviously function, yet they have different ship names or identities.

Constitution is not identity

What Aristotle implies is that the materials out of which the ship is made are not the same as the thing itself: the ship is more than the sum of its parts. That sounds an awful lot like systems thinking…

Systems thinking

Donella Meadows defines a system as a set of elements that are interconnected in such a way that they achieve the system’s function. These elements and interconnections tend to be responsive to the system’s environment through feedback loops.

For instance, a ship is a collection of wooden planks, sails, ropes, nails, and so on that are joined together in a certain way to make a seaworthy vessel. In a similar vein, a human is a system whose goal is to replicate, or at the very least survive. The cells in the body are connected through the nervous system by means of electrochemical signals to achieve that goal. Or in the words of developmental biologist Michael Levin:

Each of us consists of a huge number of cells working together to generate a coherent cognitive being with goals, preferences, and memories that belong to the whole and not to its parts.

Based on the environment, the system as a whole adapts. Near the equator, humans have darker skin, which contains more melanin and thus protects against extreme sunlight. This cellular change supports the system’s prime function: to survive in a harsh environment. Connections between elements can evolve: when new information is incorporated in the brain, neural connections are rewired. This process allows humans to learn and maintain memories of important events to increase the chances of their survival.

Systems thinking tells us that the system is indeed the same even when all the elements are gradually switched out for fresh ones, because the function and interconnections, though fluid, remain intact.

Now, what happens if we swap out the bits from the Ship of Theseus and build another vessel with the old ones? This question is essentially about teleportation (i.e. disintegration and reassembly) and was first asked by Thomas Hobbes. I leave that one for you to ponder on a rainy day.