(intro music) I'm Jennifer Wang. I'm a professor of philosophy
at the University of Georgia. Today, I'm going to talk about
the Ship of Theseus puzzle. This puzzle was recorded by Plutarch, an Ancient Greek historian,
though it's come up in many different forms over the ages. It goes like this. Theseus was this great
mythical hero of Athens, who sailed off to Crete
and slew the Minotaur, a creature with the head of
a bull and the body of a man. After Theseus came back, his ship was left in the Athenian harbor as a memorial. Over centuries, the
planks of the ship decayed and were gradually replaced. Now, it doesn't really matter
that the planks decayed, or that the ship still had masts and sails and other ship stuff too. We can simplify the story. Let's pretend that the Ship of
Theseus is a very simple ship, made of one thousand
planks and nothing more. Let's also say that the planks
are made of invincible wood, super wood, so that they never decay. In what I'll call "scenario
one", the Ship of Theseus has its one thousand
planks replaced very slowly, over the course of one thousand years. That's one plank a year. So here's the puzzle. Surely a ship can survive the replacement of one of its planks. In year one, when the
first plank is replaced, it's still the Ship of Theseus. In year two, when the
second plank is replaced, it's still the Ship of Theseus, and
so on, through year one thousand. But the ship at year zero,
the original Ship of Theseus, doesn't share any of the same parts with the ship at year one
thousand, which we can call "A." So how can A be the real Ship of Theseus? Thomas Hobbes, a seventeenth-
century English philosopher, added a twist to the story. In scenario two, a ship
repairman keeps all of the old planks of the Ship
of Theseus and uses them to build an exact replica of
the original ship, with all of the planks in the same arrangement. So in this scenario, at year one thousand, there are two exactly similar ships: the one whose planks
were gradually replaced, which we called "A" in scenario one, and the one built from the old
planks, which we can call "B." Now, A has the same claim to
being the real Ship of Theseus as it did in scenario one. But B also has a good claim to being the real Ship of Theseus. After all, it's made of the
same parts as the original Ship of Theseus, in the same arrangement. But they can't both be
the Ship of Theseus. Let's look more carefully at
the underlying assumptions that generate the puzzle. One assumption is that ordinary objects survive gradual change. This is very plausible. You can't destroy a coat just by removing one of its buttons. Maybe you then ruin the
aesthetic of the coat, but that's not what's at issue here. It's still the same coat. It's just changed a bit. The principle that ordinary
objects survive gradual change motivates the conclusion that
A is the real Ship of Theseus. Another assumption is that an
object goes where its parts go, so to speak, at least in
cases where the parts are in the same arrangements. Let's modify our scenario so
that the planks of the ship are gradually removed, but
aren't replaced with new planks. Again, the old planks are used
to build an exact replica of the ship so that, at the
end of the new scenario, there's only one ship,
the ship we called "B." Call this modified scenario
"scenario three." The principle that an object
goes where its parts go motivates the conclusion that
B is the real Ship of Theseus in scenario three. But it motivates this conclusion in scenario two as well, where
there are two ships at the end. It doesn't look like
both principles can stay. Which should go? Let's go through some possible solutions to the puzzle of the Ship of Theseus, some of which involve rejecting
one principle or the other. They all come with disadvantages. Solution one is to deny
the parts principle. This solution involves saying
that in scenario three, the ship at the end is
not the Ship of Theseus, even though it has all the same parts arranged in all the same ways. Solution two involves denying
the change principle: ordinary objects survive some
gradual change but not all. That is, sometime between the year
zero and the year one thousand, removing a plank destroys
the Ship of Theseus. The problem is that this
solution seems arbitrary. Why would removing, say,
plank number 543 destroy the Ship of Theseus, but not number 542? And at that moment, does
the ship being built out of the old planks in scenario two suddenly become the Ship of Theseus? On solution three, the
plank which destroys the Ship of Theseus is not
some middling plank. Rather, as soon as plank number one
is removed, the ship is destroyed. This solution involves denying
the change principle as well, but it offers a stronger
thesis in its place: ordinary objects never survive any change. This view was advocated
by Roderick Chisholm, a twentieth-century American
philosopher, who was inspired by Bishop Joseph Butler,
an eighteenth-century English theologian and philosopher. Butler's thesis was that
ordinary objects like ships persist only in a loose and popular sense. Whether A or B is regarded
as the Ship of Theseus ends up being something
of a practical matter. According to Butler's thesis, no
ship really ever survives any change. However, not only
is this view implausible, it implies that there
are one thousand ships where we thought there was only one, as the destruction of
each ship is followed by the creation of a new one. On solution four, neither
the change principle nor the parts principle
needs to be rejected. Rather the solution here is to say that A and B are each the Ship of Theseus. This involves rejecting
the following principle, called the "transitivity of identity": if X is identical to Y,
and Y is identical to Z, then X is identical to Z. On solution four, A is identical
to the Ship of Theseus, and the Ship of Theseus is identical to B, but A is not identical to B. According to solution five,
the Worm Theory solution, we need to change the way we're thinking about ordinary objects. Here's the idea. I introduce scenario two like this: there is a ship at year zero and
two ships at year one thousand, and the challenge is to figure
out which of the two ships at year one thousand is identical
to the ship at year zero. The implicit assumption
that worm theory rejects is that ordinary objects like ships are three dimensional objects,
where the three dimensions are spatial dimensions. According to worm theory,
ordinary objects really have four dimensions: three
spatial and one temporal. So there are no ships wholly present at year zero or at year one thousand. Rather, there is one worm-like
ship which has a part at year zero at one end, and has
A as a part at the other end. And there is another worm-like ship which has a part at year zero at one end, and B as a part at the other. The two worm-like
entities have overlapping parts at year zero. This solution doesn't require
rejecting transitivity, the parts principle, or
the change principle. After all, it's no longer
clear what claim we're making when we assert "A is identical
to the Ship of Theseus" or "the Ship of Theseus
is identical to B." A and B are not identical
to each other, but nor are either of them identical
to the Ship of Theseus. They both have the object
at year zero as a part. That is all. As you can see, accepting
any of these five solutions comes with disadvantages,
but to resolve the puzzle, it looks like we have to accept
some disadvantage or other. Subtitles by the Amara.org community
The etiquette in this sub is so awful. The top comment is a guy dismissing the problem as a 'easily solvable philosophy 101 problem.'
This is pretty universally accepted as a classic philosophy problem about identity and references. I suspect that it is so popular in intro philosophy classes because it is very accessible while not being directly settled - there are completely different answers to this question based on different theories and frameworks that are similarly supported and acceptable.
Unfortunately, instead of using this problem to educate people not experienced in philosophy on different camps of thinking in regards to frameworks that answer this question (of which the context based identity seen in the top level comment is one) - and having a debate on the pros and cons and flaws of the different theories found in the literature, this sub seems to instead be focused on shitting on any classical problem, ignoring normal philosophical for for a dismissive attitude, and ignoring the principle of charity and nitpicking at flawed phrases or word choice.
[Purely for amusement]
Shelly Kagan once told me this story about a "real life" case of the Ship of Theseus problem. I found it pretty amusing so I thought i'd share it with you.
I think this happened in New Haven though, I could be wrong. A construction company was hired to rebuild a set of dilapidated buildings. Unfortunately (for the owners), one of the buildings had historical significance and couldn't be torn down while the rest of the buildings didn't face this issue (they weren't historically significant). However, a statute in place allowed for historical buildings to be repaired. Specifically, up to 10% of the building could be repaired at any given time. So the planners put together a 10 year "repair" plan that allowed them to replace all parts of the historical building without ever running afoul of the statute.
By the end of the construction all the buildings looked identical but one of them retained a "historical" status.
I don't know if the story is true or if Shelly just made it up but I always found it amusing.
Personally, the answer I find intuitive is that "a ship" isn't a discrete thing that exists independent from its surroundings. Instead, the universe exists, and we break it down mentally to make sense of it. When we say "a ship," we're just drastically shortening "a object that (insert attributes here)."
Small children who know what a dog is will sometimes look at other animals (a bear, for example) and call it a dog. This is because a dog isn't a discrete category that exists in reality to them, but a series of traits. The bear has enough of those traits that, in the absence of any reason to think otherwise, they think it must be a dog.
So when we say "ship of Theseus," we're referring to the specific thing (again, a really blurry thing that only exists as something distinct in our minds) that Theseus (himself a really blurry thing that only exists as something distinct in our minds) rode on. But whether it's the same ship or not either means "do we think of it as the same ship?" or nothing at all, as it's only a ship in our minds.
Sorry if that's unclear. But if it is, are there any philosophers who have taken this kind of approach? Is there a name for it?
The ship is the object, not the name of the ship. If I name a pile of Rice 'Tony' the rice isn't magically imbued with some properties of Tonyness that can be removed or damaged if I switch out some grains for others. Furthermore the name for the pile of rice doesn't change just because some of the grains have been swapped out. The name is a placeholder for a set of loosely defined properties which happen to coexist. The name represents a set of conditions, which even if not perfectly met sill still hold true.
For example, if we simply add more grains of rice to the pile of rice, is it still a pile? Yes, so does it's name change now that it has more grains than it started with? Similarly would the ship change it's name just because they reinforce the mast with extra planks, or add a gangplank, or extra rope? No!
The name of the ship is a placeholder for it's historical record, but does not itself imbue properties to the object. Would renaming the ship suddenly destroy the age or history of repair for the ship? Does renaming create a new object? Of course not. It's just a point of reference for a collection of properties that happen to coexist for a while.
To really push this notion to it's limits, what if the ship was named before it was built? The collection of properties would be defined and named before they existed in one place. The plan for the ship is there but the ship isn't. Now we run up against our pile argument once, more. How many grains of rice must I add before Tony exists?
Is there a similar problem that relates to "becoming"? For example:
At what point does the food I eat cease to be food and become me?
At what point does a kitten become a cat?
a similar simile is given in the Buddhist system:
https://suttacentral.net/en/mil3.1.1
Solution 3 outright doesn't make sense. If no object can withstand replacement of its parts, then moment by moment us humans are different beings than we were the moment before. Our labels for ourselves loose meaning, even the idea of crime goes out the window. How can you prosecute someone today who did something bad yesterday when the person who did it yesterday no longer exists?
I do like solution 5 the best, though solution 4 is also thought provoking. At the end of the day, this is simply an issue with how humans label things. The ship itself doesn't care which boards it is made out of. One could easily change the label to more specifically designate the ship of Theseus, ie. 'the ship with 200/1000 original boards'.
The easy fix: The question as posed has no meaning. Identity is a psychological judgement, not a discoverable fact. The correct question is "which of the many ships would we consider the same as the original ship?" Some of them most of us would say yes, like when only one plank is replaced, the others become progressively more controversial. I might not have a single atom that I had in my body 10 years ago, but I still consider that person "me". That's a psychological judgement, not a physical fact.
This is actually one of the more interesting questions posed by the Greeks.