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Theseus' Ship Changes and Yet Remains Theseus' Ship

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Voting Style: Open Point System: 7 Point
Started: 7/16/2015 Category: Philosophy
Updated: 2 years ago Status: Post Voting Period
Viewed: 708 times Debate No: 77762
Debate Rounds (4)
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I propose to solve the paradox of Theseus" Ship by demonstrating that the essence of an object, contained within the greater equation of a relationship between it and another object, changes without ever changing the sum of the relationship. Following that I demonstrate that the only way Theseus" Ship changes are if either Theseus or the Ship is exchanged with a new object. In the case of Theseus" Ship there are two objects: Theseus and the ship. There is an additional quality which is the relationship between the two. Necessarily this relationship is an ownership imposed by Theseus on the ship. This is logically necessary as the ship doesn't contain or define the relationship. In a state of nature A does not own B. Ownership is imposed by A upon B because ownership is an act, and an act is an outward force upon the state of nature. Naturally both objects exist; the subject Theseus acts to own his ship. The ship is therefore not influencing the relationship except in being there.

This relationship can be described thusly:

Theseus' Ownership + Ship = Theseus' Ship
Theseus" Ship = Theseus' Ownership + Ship


Ship = X wooden boards, a keel, a masthead, a wheel, Y sails

Then we'd say:

(x+WB) + Ka + Mb + Wc + (y+S) = ShipD
ShipD = (x+WB) + Ka + Mb + Wc + (y+S)

In this case the variables associated after a part - such as a or b - represents the type of that object installed. For example let's say in regards to the masthead there are 5 different types of masthead available to Theseus. Mb may equal anything between M1 and M5. We won't worry about the other parts since it complicates the endeavour without adding to the argument. Finally, ShipD is the total sum of part-types and changes whenever any of the variables change.

If the ship firstly possessed M1 then the equation resembled:

(x+WB) + Ka + M1 + Wc + (y+S) = ShipD
ShipD = (x+WB) + Ka + M1 + Wc + (y+S)

Then if he replaces M1 with M2 the equation now resembles:

(x+WB) + Ka + M2 + Wc + (y+S) = ShipD
ShipD = (x+WB) + Ka + M2 + Wc + (y+S)

In this case ShipD will be a different quantity, therefore the ship has changed.

But when we're discussing how the ship relates to Theseus, Ship is summed as Ship regardless of the composition of the equation; because D never changes the fact of "Ship" or how the ship relates to Theseus.

Or otherwise,

ShipD `33; = Ship
Ship " `33; = ShipD

Therefore despite changes to ShipD:

Theseus' Ownership + Ship = Theseus' Ship.

The changes to the ship can always be expressed as a change to the ship, but not a change to how the ship relates with Theseus.

Now, you may ask "If Socrates takes Theseus' Ship, is it still Theseus's Ship". The answer is no. It could only be the case if Socrates changes the values accordingly:

Ship = Theseus' Ship,

But despite this possibility it is incorrect to state that:

Ship `33; Theseus" Ship

Since Theseus is no longer imposing his ownership on the ship Socrates may also say:

Socrates' Ownership + (Theseus' Ship - Theseus' Ownership)
= Socrates' Ownership + Ship
= Socrates' Ship

And if Socrates trades the ship for an apple,

(Socrates' Ship - Ship) + Apple
= Socrates'Ownership + Apple
= Socrates' Apple

Therefore it is logical that though the qualities of the ship can change, Theseus" Ship remains Theseus" Ship unless the relationship between Theseus and the Ship changes or if the ship is exchanged for another kind of object.


Welcome people of DDO! This debate is going to be about the famous Ship of Theseus. It is very nice to see a philosophy debate not concerned with God's existence. My opponent starts out with the following."I propose to solve the paradox of Theseus' Ship", therefore the onus is on him and I am merely going to show why his proposal does not work.

The Paradox
There are many compelling solutions, this one however is unfortunately not one of them. The reason for this is a misunderstanding of the paradox. Let's recap the paradox, shall we?

"The ancient historian Plutarch recounts the story of the famous ship of Theseus, which was displayed in Athens for many centuries. Over time, the ship's planks wore down and were gradually replaced. [...] Suppose that a custodian collects the original planks as they are removed from the ship and later puts them back together in the original arrangement. In this version of the story, we are left with two seafaring vessels, one on display in Athens and one in the possession of the custodian. But where is the famous Ship of Theseus?"(1)

This is a problem for identity, "self-sameness". It's about what criteria we have to say that something is the same over time.

My Opponent's Solution
Pro solution is at it's core the claim that what makes Theseus' ship, Theseus' ship is that he is the one claiming it as property. One can therefore change parts of the ship without breaking the ownership relation.
I think there are two possible readings of my opponent's account.

The first is that Theseus' ship is whatever is owned by Theseus and is a ship. This would miss the point entirely, since the paradox of Theseus' ship is not actually about Theseus' at all, it is about the identity of the ship itself.

Leibniz’s law: the metaphysical principle that necessarily, if a and b are identical, then they must share all of the same properties.(2)

But the ship Theseus' owns first is completely different from the ship he owns afterwards. 'Theseus' ship' is to be understood as an indexical.

Indexical: a linguistic expression whose reference can shift from context to context. For example, the indexical ‘you’ may refer to one person in one context and to another person in another context.(3)
E.g., "I like cats" when uttered by me is true, uttered by someone else it might be false.

The second, rather interesting reading is, that the ownership relation is of some privileged metaphysical significance.
I think there is much to say about this, however I am going to constrain myself to only one point, the claim that some relation like ownership is an essential property of an object.
Consider me, Fkkize, having some friend, John. 'Fjf' describes the relation 'John is a friend of Fkkize'. Say we have been friends over the past ten years. Of course I am the same person as last year, I am still Fkkize and I am presumably going to be the same person next year.
Now say our friendship ends tomorrow, and the relation 'Fjf' no longer holds, am I not Fkkize anymore? Of course I'm still Fkkize!
Similarly when considering the ship of Theseus' we can ask ourselves, is ownership, which is not even a natural kind but a social one, really necessary for the ship's identity?
Imagine Theseus' ship laying at anchor in some city. You, a super intelligent being, examine the ship in all its detail. The next day Theseus' dies and according to Pro Theseus' ship is no longer Theseus' ship anymore, but just some ship. You are unaware of this and examine the ship again, would find any differences? I think not.

He then continues to give a somewhat convoluted definite description of a ship:

"ShipD = (x+WB) + Ka + Mb + Wc + (y+S)"

This seems to be attempted translation into first order logic, but it fails right from the start.
Capital letters denote predicates (" a dog"), lower case letters from the denote subjects/ objects and lower case letters from the end of the alphabet denote variables.
X and y are not in the scope of any quantifier (invalid) and most importantly, he uses a, b and c (objects) which means this is not a description of a ship in the general sense, it is a description of one single ship. This is not what he is going for, since his solution revolves around deciding which ship is Theseus' ship by means of an ownership relation.
Here is a correct translation of the description of a ship made of wooden planks, a keel, a masthead, a wheel and a sail.

Ax((Wx & Kx & Mx & Sx) & Ey (Ty & (x=y)))
For all x, x is made of wooden planks & x has a keel & x has a masthead & x has a sail & there exists some y, such that y is a ship and x is identical to y.

My opponent presents an interesting solution, however, it faces a multitude of problems and is ultimately not what the paradox asks for.
The resolution is negated.

(2) Alyssa Ney, An Introduction to Metaphysics, p. 95
Debate Round No. 1


I_Voyager forfeited this round.


I extend all my arguments.
However I should point out a rather embarrassing mistake I made.
In my opening statement I attempted to translate my opponents definition of a ship into firs order logic. In doing so I did not produce a definition, but a definite description.
Correctly a definition of a ship, based on my opponent's, would look like this:

Ax(Tx IFF Wx & Kx & Mx & Sx)
For all x, x is a ship if and only if x is made of wooden planks & x has a keel & x has a masthead & x has a sail.

Debate Round No. 2


I_Voyager forfeited this round.


Debate Round No. 3


I_Voyager forfeited this round.


Debate Round No. 4
10 comments have been posted on this debate. Showing 1 through 10 records.
Posted by I_Voyager 2 years ago
I very much appreciate this counter-argument. You have demonstrated to me something I already knew, that I am wading into logic without properly understanding it. But I think in the end what your argument will serve to do is not to establish that my premise is entirely wrong. I think instead it will only serve to trim the fat and ignorance from my arguments. And fatty it is... But I don't think nothing will be left afterwards. I smell muscle tissue in there, somewhere.
Posted by I_Voyager 2 years ago
I don't see an edit option alas.
Posted by Fkkize 2 years ago
When you click on "Edit" there should be some option concerning voting time.
Posted by I_Voyager 2 years ago
No idea how to edit the terms of the debate.
Posted by Fkkize 2 years ago
I accept if you lower the voting time.
Posted by Alpha3141 2 years ago
Ok, cool
Posted by I_Voyager 2 years ago
Yes I do. And you're right, it's a linguistic problem. Which is what I try to demonstrate. Only by manipulating the terms can you say the boat stays the same. The boat changes, but doesn't change the terms of the relationship which leads to "Theseus' Ship".
Posted by Alpha3141 2 years ago
The problem is in definitions. People generalize things. People generalize what is "Theseus Ship". So when things continue to change in the ship, and people's explanation of what "is" the ship don't, then it gets confusing. That confusion is the problem, not the ship.
Do you get where I'm going?
Posted by I_Voyager 2 years ago
Yes, that'd be a good thing to include wouldn't it...

he ship of Theseus, also known as Theseus' paradox, is a thought experiment that raises the question of whether an object which has had all of its components replaced remains fundamentally the same object. The paradox is most notably recorded by Plutarch in Life of Theseus from the late first century. Plutarch asked whether a ship which was restored by replacing each and every one of its wooden parts remained the same ship.

The paradox had been discussed by more ancient philosophers such as Heraclitus, Socrates, and Plato prior to Plutarch's writings; and more recently by Thomas Hobbes and John Locke. Several variants are known, notably "grandfather's axe". This thought experiment is "a model for the philosophers"; some say, "it remained the same," some saying, "it did not remain the same".
Posted by Alpha3141 2 years ago
So what is the problem?
1 votes has been placed for this debate.
Vote Placed by tejretics 2 years ago
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Reasons for voting decision: Forfeit.