Against patterns: Functional similarity and the Ship of Theseus

The Ship of Theseus is a paradox that asks how the identity of an object can stay itself over time even as its material composition changes. A ship may have all of its planks replaced over time, yet remain the same ship. Similarly, humans are made of cells, and replace billions of their cells every day, yet remain themselves, for example. The economy analogously made of people, yet remains itself even as people are born and die. How can this be?

One answer to this question is that although the material composition of the object changes over time, the pattern stays the same. The Ship of Theseus is a pattern; as long as the new wooden planks reconstitute the old pattern, the ship is preserved. Humans are a pattern as well, etc.

However, there are many situations where the identity of an object survives massive changes to the pattern. For example, the owner of the ship could give up sailing and start a theme restaurant, putting part of the ship into the design of the restaurant and calling the restaurant the Ship of Theseus. The Ship of Theseus is thus preserved even though the pattern is not.

As usual, the economy gives a clear example of what otherwise is a very abstract question. The economy’s pattern is obvious and observable: the pattern of relative prices that regulate the allocation of scarce resources. We can also observe that this pattern does not stay constant. Prices changes rapidly to reflect changes in the conditions of supply and demand, and over time no part of the original pattern of prices is preserved. Yet the economy remains the economy.

All stored information is dormitive principles. Identity isn’t stored in a material substrate, but it also isn’t stored in an abstract pattern. Instead, I think it makes more sense to treat identity as a categorization decision: we categorize a changed object as an example of the same category as before when we find it useful to do so to prepare action and perception. Nothing in particular needs to be constant across any two objects—substrates, patterns, whatever—to be categorized as two instances of the same thing.

An example of this kind of categorization decision is emotion. Two instances of fear may be very different from each other: in one case, you may be afraid of a predator animal chasing you, causing you to widen your eyes and run away; in another case, you may be afraid of your boss evaluating your work, causing you to hold very still. You categorize them both as fear because there’s some functional similarity between them that makes it useful to categorize them as the same object—something that helps you bring lessons about action and perception from one instance to the other.

You could think of the category “fear” as being the order over all the instances of fear. That order is the pattern that makes fear what it is. However, that pattern is not fixed in any way. It changes as instances are added to and subtracted from the category, and as changing goals and internal and external constraints change the order over the instances. The category itself is not even fixed at any point in time but is constructed in an ad hoc fashion in the moment.

I think it’s the same with other categorization decisions. Whether you choose to call something the Ship of Theseus is a categorization decision based on some functional similarity. That functional similarity could have something to do with a particular substrate, or a particular pattern, or anything else. But nothing in particular need be preserved over time for a thing to remain itself—otherwise, a concept could die of old age.