# What is the Basis of Object Identity?

## Figure out your own best solution to the Ship of Theseus Problem

Consider the difference between the statements "this is the same car" and "this car is the same". Suppose your car has been in the garage getting the engine overhauled and otherwise tuned up. When you go to the shop, the car you pick up is the same car you dropped off (otherwise, they won't let you take it away), but that car is not the same as it was better (it will perform better in various ways).  Or suppose your friend Jimmie Dale rolls up in a loud powerful car with all kinds of scoops, vents and spoilers. You say, "wow, you got a new car", but Jimmie says, no, this is the same car I had before, I've just had a lot of work done on it". When he says this, he is claiming that the car he has now, which is physically continuous with the car he had before, has the same object identity as that car he had before.

This topic is only about object identity. If you write about other forms of identity, you are off-topic.

Note: Further new material (in red) added on Oct 26, 2023.

Please make sure that you pay at least some attention to the idea that physical continuity (AKA "Spatio-Temporal Continuity") is actually the best solution to this problem. (I'm getting tired of reading papers that ignore physical continuity, or which assert that it isn't the basis of object-identity while actually relying on physical continuity to make their favorite theory seem to work.)

First, let me discuss the issue of object identity. Suppose your grandpa owns an antique pocket watch that he has willed to you. (Call this "watch 1".) Suppose he keeps it in a safety deposit box in a bank. Suppose also that, unknown to you and Grandpa, a man called Smith keeps an exactly similar watch (call this "watch A".) in another safety deposit box in the same bank. Suppose Grandpa periodically takes you in to the bank to look at his watch, so you get to know the appearance very well. Now finally suppose that your grandpa, alas, dies and two untoward things happen in the bank. First, a clerk accidentally drops Grandpa's watch and it receives a long scratch across the back (Call the watch as it exists at this time "watch 2".) and second, when you come in to pick up your bequest, the bank manager makes a mistake and hands you a different watch, (Call this "watch B".) a watch belonging to a man called Smith that just happens to exactly resemble Grandpa's watch in every respect, and so you take it to be Grandpa's watch, and for the rest of your life you carry this watch ("watch B".) around in the happy belief that this is the watch your grandpa owned, even though it actually is not the same watch.  Meanwhile, Smith collects the other watch, ("watch 2".) and, not noticing the scratch, takes away Grandpa's watch in the belief it is his own.

So there's two watches. There's the watch that Smith now holds, which is actually the same watch your grandpa used to own, even though it is different, owing to the scratch. And there's the watch you now hold, which is not the same watch your grandpa used to own, even though it is physically the same in every respect.

Does this story make sense to you? Or do you find yourself saying things like, "oh no, watch B is actually Grandpa's watch", or finding some other problem with the story.

When the Ship of Theseus problem asks, if some ship is the same ship as the ship Theseus used to sail, it is asking if it is that ship in the sense that the watch held by Smith, with the scratch, is the same watch that your grandpa used to own. It is not asking if it looks the same, feels the same, sounds the same or smells the same, it is asking if it is the same ship. (Remember, this is only about the basis of object identity, not social identity, or historical meaning.)

Physical Continuity

Before you start, you should get clear on the concept of "Physical continuity". This is the property of being the same coherent discrete object over time.

In the story of the two watches, watch 2 is physically continuous with watch 1, while watch B is not physically continuous with watch 1. In fact, physical continuity is the only thing that connects watch 2 with watch 1, so if you think watch 2 is watch 1, physical continuity is your only reason for thinking that they're the same watch.

Human bodies are physically continuous because although they grow and change over time, this is always because of small quantities of material, contained in food, drink, and air being added to the body, and other bits of material leaving the body as exhalations, discarded skin and hair, and other ways. Thus the body you have now is physically continuous with the body you had when you were born, and indeed, with the fertilized ovum you were just after you were conceived, even though the vast majority of atoms now in your body were not there at that time.

<Added 3/28/24> For instance, the 1894 Benz Velo in the Toyota automobile museum in Nagakute city has physical continuity with the 1894 Benz Velo that finished fifth in the world's first automobile race. (Most people would say that the one in the museum is the same car as the one that came fifth in the race.)

If you're still not entirely sure what the issue is, this Video might help.

When you think you have a good understanding of the issues involved in the Ship of Theseus problem, take some more "think" time do your best to come up with the most logically justifiable answer you can think of. When you have thought about the issue, write a paper explaining the problem, explaining what you think about the problem, and saying exactly why you think what you think.

Practical solutions are preferred as opposed to arbitrary abstract, or speculative solutions that would never be used for ordinary objects in real life.

Alternate assignment: (Rewritten 11/3/22) Remember Grandpa's watch? Turns out that Smith, the owner of the other watch (the physically continuous with one you have) has found out about the switch, which is verified by security camera footage, and wants his original watch back. You don't want to swap, and don't want to believe that the watch you have isn't Grandpa's, so he takes you to court. You go into court with Smith, each believing that the watch they hold is your grandpa's watch, and that the watch the other holds is Smith's watch..

You hold a watch that is physically continuous with the unscratched watch Smith originally deposited at the bank for safekeeping.
Smith holds a watch that is physically continuous with the scratched watch Grandpa originally deposited at the bank for safekeeping.

Now, what rule should the judge use to decide which watch is yours, and which is Smith's?

Should he decide that the watch Smith has, the one that has physical continuity with the watch your grandfather owned is your grandfather's watch, or should he decide that the watch you have, the one that you believe to be Smith's watch, but Smith believes to be Grandpa's watch is Grandpa's watch?

<Added 4/4/24> To make things simple. I suggest that you think about whether physical continuity is the basis of object identity. If you decide it is, write a paper explaining both concepts, and saying why you think identity is based on continuity. If you decide it isn't, write a paper saying what you think is the basis of object identity, and why that (and not physical continuity) is the real basis of object identity.?

After you've thought this through from all angles, write a paper explaining which rule you favor (continuity, belief, or whatever) and why you reject the opposite rule.

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