Tag Archives: composite

The Ship of Theseus

2 Mar


Hello everyone! I know I have not done anything here for awhile, and it is for a good reason. My plan here from now on is to only post here a few things I have already written for school or other reasons, or to only post when I have extreme leisure time available.

I am currently in the process of beginning a book I have decided to write. This involves a strikingly different metaphysical theory inferred from an in depth analysis of the consciousness. This will either make me post here even less or, make me post here more. If you want more frequent yet shorter things from this crazy brain of mine you can follow me on tumblr:


below is an analysis of the metaphysics of identity of the puzzle of the ship of Theseus.


When Theseus, hero of Athens, last sailed his ship and left it in the harbor in Athens, the ship was left there long after his death. When the ship’s planks decayed to a point, it was renovated with new planks so Theseus’ ship would be maintained. The history of that ship led to the puzzle that has caused debate among metaphysicians as to the identity of the original ship and where the identity was after the original ship was renovated. The original ship was renovated one at a time with a new plank replacing an old decayed plank. This was done until a new renovated ship remained. For the purpose of the puzzle, the action of placing the old decayed planks of the old ship in a warehouse and then reconstructing a ship exactly the same with those same old planks is discussed also. This leads to there being two ships (one reconstructed and one renovated) and a puzzle as to which one is the ‘original’ ship that Theseus sailed. This puzzle is useful in debate for metaphysics of identity between particulars (identity of a thing to itself and identity of a thing to other things based on principles like Leibniz’s law). There is debate between people that think that the original ship is the renovated ship or the reconstructed ship for a few good reasons. One large question is as to whether an object’s identity survives the replacement of the object’s parts, and another is to whether objects can maintain identity in intermittent existences. These and other things matter a lot in arguing for any position that could possibly solve this puzzle.

Since no one conclusion can be achieved that solves this puzzle without some further objection, both arguments are worth exploring. At present, I will explore both sides of the argument yet argue for the reconstructed ship being the original. I will argue the following argument and refute its objections:

  1. If x has exactly the same parts as y, then x=y
  2. The reconstructed ship has exactly the same parts as the original ship
  3. Therefore, the reconstructed ship = the original ship

This argument obviously favors the reconstructed ship being the original ship, but objections and counter-arguments need to be taken into consideration before proclaiming this argument to be a better solution to the puzzle.

Before going through the argument premise by premise, it is worthy to note that this puzzle as it corresponds to metaphysics and identity is important as the ships’ numerical and qualitative identities. Objects are often understood as composite objects because of how many parts are understood as one composite object together as a whole. Two objects, or an object and itself, are numerically identical if the objects as composites are the same (e.g. a banana is numerically identical to itself when it goes from its green color to yellow). Two objects are qualitatively different when parts or qualities within a composite object are different between two objects or an object and itself at a later time. The banana is not qualitatively identical to itself between its time as a green banana and its time as a ripe yellow one. Keeping these terms in mind going further, it is also worthy to note that this argument for the reconstructed ship is valid as its conclusion follows from the two premises.

The first premise (if x has the same parts as y, then x=y) is generally a common sense principle. Lowe in A Survey of Metaphysics uses examples of ancient artifacts and the restoration of them. When an artifact is restored (taken apart then put back together where x is the artifact before disassembling and y is the artifact after reassembling), the newly reconstructed artifact is considered still the original artifact that was excavated. Numerical identity seems to subsume qualitative identity in that the composite whole of an object gets its numerical identity from the parts that make it up. The parts of an object matter to the whole identity of an object, therefore, this premise is favorable. Objections come from the possibility of a composite object being disassembled (i.e. the ship of Theseus) and then reassembled. X and Y would still have their same parts, but their identity may have been lost between disassembling and reassembling. One might object by asking where the existence of the object went from the time the object was disassembled up to the time it was reassembled. The replacement of an object’s parts brings further objections.

The second premise (the reconstructed ship has the same parts as the original ship) is simply an example of the first premise that states that when an object has the same parts as another object then those two objects equal each other. Since qualitative identity is seemingly subsumed by numerical identity, the reconstructed ship will end up debatably having the same numerical identity as the original ship. One large question that divides the arguments of the puzzle of Theseus’ ship is whether or not an object’s identity can survive the replacement of its parts. One arguing that the reconstructed ship is the original ship is saying that an object’s identity cannot survive the replacement of parts. On this view, once the parts are replaced an intermittent existence is allowed for the object as its original parts are disassembled where the object still exists but is simply on existential hiatus. This violates a common sense principle because an intermittent existence is sometimes thought of as a ‘ceasing to exist’ and a ‘coming back into existence’ allowed for the object that violates many things philosophers have already stated. These two big questions create the dividing line between the two sides of the puzzle.

From the previous two premises, it is easy to see how this conclusion follows: Therefore, the reconstructed ship = original ship. This conclusion to the puzzle is arguable because it is numerically identical as well as qualitatively identical to the original ship. It has all the same parts making the composite object equal to that of the original ship. The renovated ship has both of these kinds of identity but has less qualitative identity because of the set of different parts it was given during renovation. Concluding by saying that the reconstructed ship is the original is saying that the object’s identity cannot survive the replacement of parts because of the changes of qualitative identity. Concluding this is also saying that intermittent existences are allowed and are not equivalent to a contradictory ‘coming into existence’ and ‘ceasing to exist.’ This conclusion is also saying that the original ship cannot be both renovated and reconstructed ships because one identity cannot be in two spatial locations at once. This is also saying that it cannot be neither the renovated nor the reconstructed ship because that conclusion would cause one to stop using general common sense.

Whether one thinks the original ship is the renovated or the reconstructed it comes down to whether that person thinks objects can have intermittent existences and whether object’s identities can survive replacement of parts. Having discussed this argument and its objections it is clear why one would argue either stance. My argument is in agreement with the current argument discussed. When thinking about metaphysical identity at all it is easy to see how and why numerical identity subsumes qualitative identity. Because of this, I do not agree that the object’s identity survives the replacement of its parts. The renovated ship after replacement has differences of qualitative identity from the original ship because of the entirety of different parts even if renovated in the same structure as the original ship. The parts of the ship contribute to its qualitative identity. Furthermore, I agree that objects are allowed intermittent existences and during existences such as these a composite object does not cease to exist or come back into existence when restructured. When the original ship was renovated, each part removed from the ship was taking a little bit of the original ship’s identity little by little.  The identity of the original ship stood with the old decayed planks in the warehouse that were reconstructed. All of this comes down to the argument that the identity of the ship is in the planks that made up its parts and the whole composite object. The renovated ship with new planks is a new composite object with new parts and thus a new identity. Even though there are objections to this stance, one identity cannot be identical to a qualitatively different one.