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Theseus' ship - what is your view?

  1. Jan 19, 2006 #1
    This is the story:

    Theseus is famous in Greek mythology as the slayer of the Minotaur, a half-man, half-bull monster who lived in the Labyrinth in the island of Crete. According to Plutarch, the ship in which Theseus sailed back to Athens was preserved for many generations, its old planks being replaced by new ones as they decayed.

    Now suppose that a few hundred years later, all the original parts of the ship had been replaced, one by one, so that none of the original ship remained. Is the preserved ship still Theseus' ship? Or is it a copy? And if the latter, then at what point did it cease to be Theseus' ship?

    This problem involves the notion of identity, of what we mean by something being the "same" object. Suppose that we regard the final ship as Theseus' ship. What if all the old planks, nails, etc., had been stored in a warehouse and someone put them back together again. Would there then be two Theseus' ships?

    What is your view?
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  3. Jan 19, 2006 #2


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    Well, I don't know how Theseus came into this; I learned the problem as great-grandpa's gun. "That's my great-grandpa's gun hanging on the wall. Grandpa replaced the stock, and daddy replaced the lock, and I replaced the barrel, but yep! That's great-grandpa's gun!"

    Aristotle had something to say about this. See form and substance.
  4. Jan 19, 2006 #3
    Try it with a pair of socks. You lose one at the laundromat and replace it with another one you found there. Is it your pair of socks or someone else's? :uhh:
  5. Jan 19, 2006 #4
    This idea is no different than the effects of the passage of time on the human body. As time passes, cells in the body die and are replaced by other cells. Yet, after 7 or so years, when pretty much everything except nerve cells have been replaced, the self is still the self. It is the whole that makes something...something. My body is still my body even after many years, regardless of the fact that "parts" of the body have been replaced.
  6. Jan 19, 2006 #5
    this question, pivoxa15, is really more valuable than it is getting credit for, i think. many posts have replied in, what one may consider, a less than genuine or adequate way. i will not attempt to answer this question, directly, but i will suggest a reason why many have "dodged" the question thus far.

    i would like to pose one further question, in response:
    how can we think ourselves capable of answering a question, about the nature of a thing (which i perceive this question as being... fundamentally), when we are not yet certain of what it is that "i" am?

    we are looking to satisfy the nature of theseus' ship as a conceptual or categorical definition. this is not different from the conceptualization that we apply to "i". is asking the question about the nature of theseus' ship any different from asking the question about the self? essentially?

    i will say, "no".

    further, i propose that the doing, of those who may have "dodged" your question, is an extension of the uncertainty, that those have, in knowing who they are.

    again, how can we know what something is, if we do not yet know what "i" am? in light of daveb's reply, what is the "whole"?

    this is now a metaphysical inquiry.
    to answer the question about the nature of the ship, is to, covertly, make a claim about the nature of the self.
  7. Jan 19, 2006 #6

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  8. Jan 19, 2006 #7
    ...where Mattius_ finally spoke and got it straight, I see. When you change one sock in your pair, you don't have the same pair of socks anymore. You have part of the original pair, plus something else. It's still a pair of socks, just not the pair you started with. Same for the boat.
  9. Jan 19, 2006 #8
    I think one major problem is language. Our language was invented to help make people's lives easier when living with other people. It was not designed to help us solve all the problems in the universe. Deeper thinkers will find problems in our language such as the notion of identity and many other properties. These confusions are embedded in our language from ancient times. That could be one reason why physics is done in mathematics rather than an ordinary language (that is not to say there aren't any debate in the foundations of mathematics but it is much less than in English).

    It is convinent to talk about a whole but sometimes (if you analyse it carefully enough) the notion can break down as we have seen. So the problem is in our language.
  10. Jan 19, 2006 #9

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    I have the Mazda of Theseus. I have replaced virtually everything but the steering wheel. And yet, it's still my same old car.
  11. Jan 20, 2006 #10
    It may still belongs to you but it's not the same as when you bought it. It only seems this way when you choose to simplify by disregarding all non-original components.

    Years ago I bought a new car from Ford. At the time they provided a lifetime guarantee on all replacement parts on their new vehicles. I figured that if I had every single part serviced and replaced, the whole car would be on a lifetime waranty! :biggrin: I didn't do it of course, but this thread reminds me of this. I would certainly not end up with the car I bought if I had done this. As soon as you change the original, it's no longer the original even if you retain ownership under the law.
  12. Jan 20, 2006 #11
    ever think that there's one pair of socks? or, that there's one boat? ...... that there's one self?
  13. Jan 20, 2006 #12

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    I love your thinking, Orefa. And your clear examples. You are an astute logician. :smile:
  14. Jan 20, 2006 #13


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    Re: Form and Substance and 'sameness.'
    How about say, a corporation? After so many years, let's say not only
    has there been a complete turn-over of employees, but let's say all the original assests have been sold or traded for a completely different set of assests. It's still ''formally' the same corporation but it is now 'substantially' different.

  15. Jan 20, 2006 #14
    The least workable definition, although the most sound, is that each time there is any change to the ship, it becomes something different. So yes, a dent somewhere, and it's not the same ship anymore.

    Though this seems unreasonable, since if an atom that is part of the ship decays, or even loses an electron, it is technically something else.
  16. Jan 20, 2006 #15
    Not really, not really, and yes of course; why do you ask?
    Thank you!
    Same thing. But you have to remember that a corporation is an entity defined by legal documents, not by its assets. As such, it only changes when the legal documents that define it change.
    It is quite reasonable. Everything that exists exists as a result of the transformation of previously existing elements. Nothing is created, nothing is lost, all is transformed. When does a wooden plank become a table? When it undergoes enough changes to fit a new definition. It may be the "same" piece of wood but it ceases to be a plank. Eventually the table ceases to be a table too because it becomes firewood instead, then smoke and ashes... The only item I can think of that maintains its identity is the universe itself since by definition it is all that exists. But since all its parts change constantly then each one can only have a precise identity at a precice moment in time. For practical reasons though, we commonly loosen our understanding of identity so we don't spend all our time tracking atoms.
  17. Jan 20, 2006 #16
    Suppose someone was to assemble a car from all the old parts of the original Mazda. So you would have a car that is exactly the same as your old Mazda except for the steering wheel and some minor parts.

    Now you have 2 Mazdas. One with only the original steering wheel and most of the remaining parts different to the original car. The other Mazda has all your old parts except a new steering wheel and some other new minor parts. Which Mazda do you cliam is your orignal car now?
  18. Jan 20, 2006 #17

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    The one possessing a VIN number that matches my title. :smile:
  19. Jan 20, 2006 #18
    Neither. The original car was made of all its original parts so neither of these two cars qualifies.

    Ownership is a different (legal) matter.
  20. Jan 20, 2006 #19
    we have posts (so far) that conceive the ship as composed of atoms. this view is not different from the view where the ship is conceived as being composed of planks of wood and other parts. the point is the same in both views: that all "things" are composed of various parts which, when altered, alters the "object" in such a way as to only be conceived of as a continually existing entity in a very abstract way.

    we are currently discussing the nature of this "abstract" notion.

    which brings me precisely to my previous (now deleted... lol) post. only now, i am careful to avoid great depth... or any at all, really. so i will give an observation, and be done.

    we are really talking about whether there are entities that have "continual existence", through time; whether one conceptual entity can be said to exist objectively (as an "object"), independently, from one moment to the next.

    this is the fundamental point of this discussion, i think.

    i will say:
    some thing only seems to exist independently, in space and time.
    because some thing exists in space, it is subject to time and change.
    if something is absolutely subject to time and change, in respect to spatiality, then it becomes impossible to say, exactly where one thing "begins" and "ends" and where another "begins" and "ends".

    this is elementary for some, but requires deep contemplation for most.

    oh well, "what is to be will be".
  21. Jan 20, 2006 #20

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    yup. Right you are. Wrong am I.
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