The ship of Theseus

The ship of Theseus, 

also known as Theseus’ paradox, 

is a thought experiment that 

raises the question of 

whether an object that has had 

all of its components replaced 

remains fundamentally the same object.

Theseus’ ship was a useful thought puzzle to illustrate the seemingly unsolvable paradox of who we are. Who are we in the face of our growth and evolving identity?

The paradox asks whether a ship - the ship of Theseus - that had been restored by replacing every single wooden part remained the same ship.

Everything in the 3D world changes, transforms, and renews. 

The world as we see it today is totally different from the world that existed 10, 100, or 1000 years ago. Nature continuously blossoms and dies. 

Yet, there is a matrix of continuity.

Consider having two photos side by side of the same person, one picture shows the person in old age and the other picture shows the person in their youth. 

How is the person in the two pictures the same, and how are they different?

The body continually regenerates cells, and science tells us that after seven years, the entire body no longer has any of its original cells. Therefore, the human body, just like the Ship of Theseus, has come to be different to its original form, because the old parts have been replaced with new ones to create an entirely new object.

The cells in our body die too, to get replaced by new ones. There’s very little of us (just some brain and muscle cells) that is the same as 10 or 20 years ago.

• Coming back to the Theseus paradox - if almost all the cells in our body are different from when we were born, can we say we are a different person? 
• Is the ship of Theseus the same ship, after having replaced every single part?

Are You Still You?

The Ship of Theseus paradox may seem like an abstract thought experiment at first, but it holds significant implications for our understanding of personal identity and the nature of change over time. As we go through life, we all experience physical, emotional, mental, and spiritual changes that can alter our sense of self. 

How do we know that we are the same person we were five years ago?

Physically, our bodies are constantly changing. 

Our cells (with the exception of some brain cells and your eye lens) are constantly dying and being replaced, and we may undergo significant changes in appearance over time. For example, we may gain or lose weight, develop wrinkles or gray hair, or undergo surgeries that alter our physical form. 

Emotionally and mentally, we may also undergo significant changes over time. 

Our experiences and relationships shape our personalities and perspectives, and we may develop new beliefs or values that fundamentally alter who we are. 

Spiritually, we may also experience shifts in our beliefs or sense of purpose over time. We may undergo spiritual awakenings or crises that fundamentally alter our understanding of ourselves and the world around us. 

The paradox asks whether we are still the same person after these changes, or if we have become someone new.

How much of our identity is tied to our physical body, our memories and experiences, and our beliefs and values?

In a sense, we are all like the ship of Theseus. 

Constantly undergoing change and evolution, and our sense of self is not fixed or static. Instead, we are in a perpetual state of becoming, adapting to new experiences and challenges. Our physical bodies and personalities do not define us; rather, it is our deeper sense of self and purpose. By embracing this fluidity and recognizing the potential for growth and transformation, we can cultivate a deeper sense of self-awareness and acceptance, enabling us to navigate life’s changes with greater ease and resilience.

According to Aristotle, the ship of Theseus is the ‘same’ ship, because the formal cause, or design, does not change, even though the matter used to construct it may vary with time.

This suggests that it’s the design, or the DNA that defines our identity; to preserve this initial design, this DNA, there is continuous change and adaptation.

While our identity is in a continuous evolution, change, and renegotiation, there is an underlying direction that our ship sails toward.

While in the ocean of life, we may drift and adapt, we must always remember where our ship is heading. Why was it initially built for, what was its purpose?

And if we get stuck in a sandbar, that’s perhaps because there are parts of us that need more expression. Exploring the different facets of our identity and bringing forward both our inner twins doesn’t make us inauthentic or contradictory. It's a natural part of the journey called life.

In Greek mythology, Theseus, mythical king and founder of the city Athens, rescued the children of Athens from King Minos after slaying the minotaur and then escaped onto a ship going to Delos. Each year, the Athenians would commemorate this by taking the ship on a pilgrimage to Delos to honour Apollo. A question was raised by ancient philosophers: After several hundreds of years of maintenance, if each individual piece of the Ship of Theseus was replaced, one after the other, was it still the same ship?

In contemporary philosophy, this thought experiment has applications to the philosophical study of identity over time, and has inspired a variety of proposed solutions and concepts in contemporary philosophy of mind concerned with the persistence of personal identity.

The account of the problem has been preserved by Plutarch in his Life of Theseus:

The ship wherein Theseus and the youth of Athens returned from Crete had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their places, insomuch that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.

— Plutarch, Life of Theseus 23.1

Over a millennium later, the philosopher Thomas Hobbes extended the thought experiment by supposing that a ship custodian gathered up all of the decayed parts of the ship as they were disposed of and replaced by the Athenians, and used those decaying planks to build a second ship. Hobbes posed the question of which of the two resulting ships, the custodian's or the Athenians', was the same ship as the "original" ship.

For if that Ship of Theseus (concerning the Difference whereof, made by continual reparation, in taking out the old Planks, and putting in new, the sophisters of Athens were wont to dispute) were, after all the Planks were changed, the same Numerical Ship it was at the beginning; and if some Man had kept the Old Planks as they were taken out, and by putting them afterward together in the same order, had again made a Ship of them, this, without doubt, had also been the same Numerical Ship with that which was at the beginnings and so there would have been two Ships Numerically the same, which is absurd... But we must consider by what name anything is called when we inquire concerning the Identity of it... so that a Ship, which signifies Matter so figured, will be the same, as long as the Matter remains the same; but if no part of the Matter is the same, then it is Numerically another Ship; and if part of the Matter remains, and part is changed, then the Ship will be partly the same, and partly not the same.

— Thomas Hobbes, "Of Identity and Difference"

Hobbes considers the two resulting ships as illustrating two definitions of "Identity" or sameness that are being compared to the original ship:

1. the ship that maintains the same "Form" as the original, that which persists through complete replacement of material and;
2. the ship made of the same "Matter", that which stops being 100 per cent the same ship when the first part is replaced.

According to other scientists, the thought puzzle arises because of extreme externalism: the assumption that what is true in our minds is true in the world. 

Noam Chomsky says that this is not an unassailable assumption, from the perspective of the natural sciences, because human intuition is often mistaken. Cognitive science would treat this thought puzzle as the subject of an investigation of the human mind. Studying this human confusion can reveal much about the brain's operation, but little about the nature of the human-independent external world.

Following on from this observation, a significant strand[who?] in cognitive science would consider the ship not as a thing, nor even a collection of objectively existing thing parts, but rather as an organisational structure that has perceptual continuity.

In Europe, several independent tales and stories feature knives that have had their blades and handles replaced several times but are still used and represent the same knife. 

1. France has Jeannot's knife, 
2. Spain uses Jeannot's knife as a proverb, though it is referred to simply as "the family knife",  
3. Hungary has "Lajos Kossuth's pocket knife". 

Several variants or alternative statements of the underlying problem are known, including the grandfather's axe and Trigger's broom,where an old axe or broom has had both its head and its handle replaced, leaving no original components.

The Tin Woodman, a character in the fictional Land of Oz, was originally a man of flesh and blood, but all his body parts were replaced one by one by metal parts. nevertheless, he retains his identity.

The ancient Buddhist text Da zhidu lun contains a similar philosophical puzzle: a story of a traveller who encountered two demons in the night. As one demon ripped off all parts of the traveler's body one by one, the other demon replaced them with those of a corpse, and the traveller was confused about who he was.

The French critic and essayist Roland Barthes refers at least twice to a ship that is entirely rebuilt, in the preface to his Essais Critiques (1971) and later in his Roland Barthes par Roland Barthes (1975); in the latter, the persistence of the form of the ship is seen as a key structuralist principle. He calls this ship the Argo, on which Theseus was said to have sailed with Jason; he may have confused the Argo (referred to in passing in Plutarch's Theseus at 19.4) with the ship that sailed from Crete (Theseus, 23.1).

In Japan, the Ise Grand Shrine is rebuilt every twenty years with entirely "new wood". The continuity over the centuries is considered spiritual and comes from the source of the wood, which is harvested from an adjoining forest that is considered sacred.

Two-faced Janus, depicting old age and youth, 

by unknown Italian sculptor, late 18th century, via Hermitage Museum

  One of the more interesting challenges 

to the position that 

continuity of mental states 

characterizes a human being 

is the question of 

transitivity of identity. 

This discussion becomes far more interesting when we stop talking about ancient ships and start talking about human beings. 

• Every person changes over time. 
• We grow from infants to old people. 
• What properties does a three-year-old have in common with their eighty-three-year-old self? 
• These philosophical questions are called the problems of personal identity. 
• What are the properties that make up a particular human being? 

We are not the same person we were several years ago. Nevertheless, we are still considered the same person.

  

Some thinkers push the notion that a person is essentially their body. 

We each have different bodies and can say that every person is identified with their body. By postulating that a human being is their body, we are subject to the same insoluble questions that we faced with the ship of Theseus and other physical objects. 

Our bodies are in constant flux. Old cells die and new cells are constantly being born. In fact, most of the cells in our body are replaced every seven years. 

This leads to hundreds of questions that philosophers have posed over the centuries. 

Why should a person stay in jail after seven years? After all, “he” did not perform the crime. It was someone else. Should a person own anything after seven years? The old person bought it. 

In what sense is a person the same after having a limb amputated? 

Science fiction writers are adept at discussing challenging questions like cloning, mind transfers, identical twins, conjoined twins, and other interesting topics related to the notion that a person is the same as their body. 

1. When an ameba splits, which is the original and which is the daughter? 
2. When your body loses cells it loses atoms. These atoms can go on to belong to others. Similarly, other peoples’ atoms can become part of your body. 
3. What about death? We usually think in terms of the end of a person’s existence when they are dead even though the body is still there. Sometimes we use sentences like “She is buried there” as if “she” were still a person. And sometimes we use sentences like “His body is buried there” as if there is a difference between “him” and his body. 

In short, it is problematic to say that a human being is identified with their body.

Other thinkers favor the notion that a person is really their mental state or psyche. 

After all, human beings are not simply their bodies. 

A person is more than a physical object because there is thought. 

To such philosophers, a person is a continuous stream of consciousness—they are memories, intentions, thoughts, and desires. 

This leads us to ask other insoluble questions: 

1. What if a person has amnesia? Are they the same person? 
2. Doesn’t a person’s personality change over time? 
3. Who is the real you: the one who is madly in love with someone or the one who is bored with the same person two months later? 

Literally hundreds of questions can be posed about change in a person’s thoughts, memories, and desires. 

Again, philosophers and science fiction writers have become quite adept at describing interesting scenarios that challenge our notion of a human being as a continuous stream of mental states. These scenarios are concerned with Alzheimer’s disease, amnesia, personality changes, split-brain experiments, multiple personality disorders, computers as minds, and so on. 

There are also many questions along the lines of the mind-body problem. 

How much is the mind—that characterizes a human being— independent of the brain, which is a part of the body?

One of the more interesting challenges to the position that continuity of mental states characterizes a human being is the question of transitivity of identity. 

My mental states are essentially the same as they were ten years ago. That means I am the same person I was ten years ago. Furthermore, ten years ago, my mental states were essentially the same as they were ten years earlier. Hence the person I was ten years ago is the same as the person I was twenty years ago. 

However, at present, I do not have similar mental states to those I had twenty years ago. So how can it be that I am the same person I was ten years ago, and that person is the same as I was twenty years ago, but I am not the same as I was twenty years ago?

Yet another option is that everyone has a unique soul that determines who they are. 

Avoiding the questions of the definition or existence of a soul, let us concentrate instead on how this answers our question of the essential nature of a human being. 

1. Assuming the existence of a soul, what is the relationship between the soul and the body? 
2. What is the relationship between a soul and a person’s actions, psyche, and personality? 
3. If there is no connection, then in what sense is one soul different from another soul?
4. How can you differentiate between souls—or identities, for that matter—if they have no influence over any part of you? What would the purpose of an identity be? 
5. If, on the other hand, a connection exists, then does the identity change when the body, actions, psyche, or personality changes? 
6. Is the soul in flux? 

If the identity does change, we are back to the same questions we had previously asked: 

1. Who is the real you? 
2. Are you the one with the soul prior to the change or are you the one with the changed soul?

Most people probably have an opinion 

representing some hybrid version 

of all three ideologies: 

a person is a composite of 

body, mind, and soul. 

Nevertheless, all schools of thought are somewhat problematic.

  

Zhao Chen

 

You’re going from point A to point B and then things fall apart catastrophically and you’re here. […] So you can think: Well, I’m who I was, that would be one kind of identity, I’m the person I thought I was. That blows apart. Then you’re in this terrible place and you think, oh, I’m the sort of person who’s in this terrible place. That’s another form of identify.

And then you can think: I’m not the old person or the person who was in the catastrophe, I’m the new person. But the problem is the new person can fall apart, too.

But then there’s a third way of thinking. This is a better way of thinking. I’m not this, or this, or this, I’m the process by which [the transformation] occurs. I know something, it’s not quite right. It collapses, it causes trouble (the collapse), but I regroup, I learn, I regenerate, I put myself back together and it happens again and it happens again. But each time it happens, maybe, you’re a little wiser, you’re a little more put together.

Jordan B. Peterson

Who are we in the face of our growth and evolving identity? 

Peterson conceptualises our identity as a story and suggests that we therefore shouldn’t look at ourselves as fixed states. Rather our identity is the driving force behind the transformation between the states — for the worse or for the better.

I can’t help but notice similarities to the Zen idea of the eternal now. It posits that the past and the future are mere illusions as there is only what happens in the never-ending moment. Paradoxically, this reduces our story to a single state. Reality is experienced only in the present. The past is in your mind only. The future is speculation.

Peterson’s thoughts are also a nod to personal agency and responsibility. 

In his reading, identity would be less defined by where who, or what we are at any given moment. But by how we respond to those states. That is the decision we make to transcend our inevitable suffering and manage to grow in spite of it. Again, it would make for a good Zen story in that it’s precisely our insufficiencies that cause transformations through a ceaseless effort to make things better than they are.

What makes this interpretation resonate? 

It’s no secret that we tend to be harsher on ourselves than on others. After all, we can’t escape the vivid memories of all the worst versions of our past selves. 

With other people, however, I found that I rather tend to focus on the trajectory they chose for their lives. What I tend to see, respect and admire in people is their story of having been to hell and gotten back out alive. In other words, I see in them the transformative spirit that drives them.

With that in mind, we should be able to put Theseus’ ship to rest. 

The thought experiment seems to be less about the rotten planks and more about the act of taking responsibility for replacing them. 

It’s about the willingness to respond to inadequacies and to let go of insufficiencies, including the ones that gradually built over time. 

Had the ship not been cared for, the vessel would’ve eventually ceased to exist due to natural decay. Granted, ships don’t have agency, which is why Theseus has to act as a proxy.

Even though in the original story the king has long passed away, we could argue that the wood was replaced in the spirit of preserving his legacy. Arguably, this wouldn’t have happened if Theseus’ deeds hadn’t had such a profound impact on Greek society. 

The replacement of the rotten planks becomes a symbol of responsible behaviour. 

The same goes for our shipbuilder. It’s not about where the planks came from. But about his efforts to turn the discarded material into something new and useful. 

Fontes: 

Noah Levin, in“Introduction to Philosophy and the Ship of Theseus.”

Noson S. Yanofsky, in "The Outer Limits of Reason: What Science, Mathematics, and Logic Cannot Tell Us" 

Jordan B. Peterson,in " 12 Rules for Life Tour"