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Free Will
Mental Causation
James Symposium
The Ship of Theseus

The Ship of Theseus was a famous vessel

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

In his De Corpore, Thomas Hobbes followed up an ancient suggestion that the ship's original planks might have been hoarded by a collector on land and reassembled, once every part had been replaced. Hobbes offered the reassembled ship as the true original. But he may have had his tongue in his cheek about the ambiguous use of language in truth claims. It is the true original, qua material, but not qua a functioning ship.
Information philosophy resolves the paradox
From an information philosophy perspective, the Ship of Theseus is just a quibble about naming. But the full facts of the matter provide the information to name a ship uniquely.

We have perfect information about the constituting planks, especially if they are carefully distinguished and stored for reassembly of the original planks as a museum copy (presumably the ship reassembled from old planks will not be seaworthy).

We have perfectly understandable and meaningful names for all the parts in this problem. We have the original ship. We have for example original plank 224, replacement plank 175, etc. We have the repaired ship with specific replacement planks in position. We can keep a diagram showing where all the planks fit. Finally we have the reassembled ship. We can see two numerically distinct ships (or at least collections of ship parts) at all times

The comparable problem of identifying parts of an organism, - specific cells, even atoms, is extremely difficult if not impossible. The exact boundaries of organs and limbs are vague, etc.

So apart from denials that composite inanimate objects exist at all, where is the deep metaphysical problem?

If it is the problem of identity through time, the information philosophy solution is straightforward.

  1. Material constitution is not identity. So the specific planks, mere substrate, are not what the Stoics would have seen as a "peculiarly qualified individual."

  2. It is the arrangement of functioning material parts that makes a functioning ship. As the Stoics would have said, it is both material substance and immaterial qualities (the Skeptics suspect two things in one place?) taken together that constitute the ship.

  3. Just as Dion can survive the loss of a foot, just as human beings survive the almost complete replacement of their atoms and molecules - several times in a lifetime, so the ship can survive any number of working replacement planks.

  4. In the Academic Skeptic version of the Growing Argument, any change of material produces a numerically distinct ship. But the Stoics say this is just destruction and generation, not true growing. Real growth and decline happens to the entity whose identity we can trace through time by its bundle of peculiar qualities.

  5. And there is one implicit quality that is ignored in the paradox, an important piece of information that identifies a unique ship. Only one of these ships carries Theseus and the youth of Athens, traveling back and forth across the Aegean.

  6. Whatever the specific planks in use, the one that is uniquely The Ship of Theseus is the one sailing the Aegean down even to the time of Demetrus Phalereus.

How to Make Two Ships Out of One.
Most of our metaphysical puzzles start with a single object, then separate it into its matter and its form, giving each of them names and declaring them to be two coinciding objects. Next we postulate a change in either the matter or the form, or both. It is of course impossible to make a change in one without the other changing, since we in fact have only one object.

But our puzzle maker asks us to focus on one and insist that the change has affected the status of only that one, usually claiming that the change has caused that one to cease to exist. This follows an ancient view that any change in material constitutes a change in identity. But the modern metaphysicist knows that all objects are always changing and that a change in identity may always preserve some information of an entity. The puzzle claims that an aspect of the object persists if the relative identity, or identity "in some respect" has not changed.

To create a paradox, we use two of our three axioms about identity,

Id1. Everything is identical to everything else in some respects.

Id2. Everything is different from everything else in some other respects.

We (in our minds) "pick out" one respect whose identity persists over time because of Id1 and a second respect which changes in time because of Id2.

In cases of coinciding objects, we start with one object that both persists and does not persist (in different respects, of course), the very essence of a paradox. We call them different (coinciding) objects to create the puzzle.

In our case of the Ship of Theseus, we actually create two ships over time. We can look at this as creating two sets of coinciding objects. In each case, we focus on the persistent aspect and ignore the changes.

One persists as a functioning ship, ignoring the changes in matter (the planks). The other persists over time with respect to its matter. They both can claim to have preserved their identity over time with the original ship, but in different respects, the first qua functioning ship, the second qua material.

In the first case, we are asked to ignore the changes in matter. In the second case and the more sophisticated Hobbes formulation, we ignore the loss of function and we ignore the loss of form until the rebuilding of a non-functional ship with the form of the original.

In other puzzles, we are asked to make a change in only the form (The Statue and the Clay) or only in the matter (The Debtor's Paradox), or in both matter and form (The Growing Argument, The Problem of the Many, or Dion and Theon). A focus on the information always finds identical changes in both the matter and the form. The paradox maker focuses on one and ignores the other.

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