Theories of Identity Over Time

TL;DR

You'll learn different theories explaining how things stay the "same" even when they change. These ideas help us understand personal identity, objects like a ship, and even complex systems. There's no single easy answer, but exploring these perspectives clarifies how we think about persistence.

1. The Mental Model

Imagine your favorite childhood toy; it's broken, repaired, maybe even repainted over the years. Is it still the same toy? This core question – how does something keep its identity through changes – is what these theories try to answer.

2. The Core Material

When we talk about "identity over time," we're not just thinking about people. It applies to everything: a river, a country, a company, or even a software program that gets updated countless times.

2.1 The Ship of Theseus: A Classic Puzzle

The most famous example is the Ship of Theseus. Imagine a ship where, over many voyages, every single plank and mast is replaced until none of the original parts remain. Is it still the Ship of Theseus? What if all the old planks were gathered and reassembled into a second ship? Which one is the real Ship of Theseus?

2.2 Core Theories of Persistence

There are a few main ways to approach this:

• Substance/Continuity Theory: This suggests that identity relies on the continuous existence of a core "substance" or a continuous causal chain. If there's a unbroken link, even with changes, it's the same thing. For you, it's the continuous existence of your body or consciousness.
• Spatiotemporal Continuity: This theory argues that what makes something the same over time is its continuous occupation of space and time. It didn't just poof out of existence and reappear somewhere else; it moved or changed gradually.
• Functionalism: Here, identity is tied to an object's function or role. If it still does the same thing, serves the same purpose, or fulfills the same organizational structure, it's the same. This applies well to complex systems or tools.
• Bundle Theory: This view proposes that an object is just a "bundle" of properties or perceptions. There's no underlying "substance." If the bundle of properties changes too much, or if a different bundle forms, it's a new object.
• Psychological Continuity Theory (for persons): Specifically for people, this theory suggests that what makes you you over time isn't your body's particles, but the continuity of your memory, personality, beliefs, and consciousness.

Let's visualize these relationships with the Ship of Theseus problem:

graph TD
    A["Original Ship of Theseus"] --> B["All planks replaced gradually"]
    B --> C["New Ship (all new planks)"]
    A --> D["Original planks reassembled"]
    D --> E["Reassembled Ship"]

    subgraph "Which is the 'real' Ship of Theseus?"
        C -- "Favored by" --> F["Spatiotemporal Continuity (same location/path)"]
        C -- "Favored by" --> G["Functionalism (same purpose/use)"]
        C -- "Favored by" -- H["Substance/Continuity (continuous existence despite part changes)"]

        E -- "Favored by" --> I["Bundle Theory (same 'bundle' of original parts)"]
        E -- "Favored by" --> J["Substance/Continuity (same *original* substance)"]
    end

2.3 The Role of Persistence vs. Constitution

It's important to distinguish between persistence (what makes something the same over time) and constitution (what something is made of at any given moment). The Ship of Theseus highlights this: the ship is constituted by its planks, but its persistence isn't necessarily about those specific planks.

For example, a statue is constituted by a lump of bronze. If you melt the statue down, the lump of bronze still exists, but the statue doesn't. Its identity as a statue was tied to its shape and form, not just the material.

3. Worked Example

Let's consider a popular software application, say, an operating system like "Windows."

1. Original Windows 1.0 (1985): Very basic, graphical interface.
2. Windows XP (2001): Major overhaul, new code, new look, many new features. Almost no original code remains.
3. Windows 11 (2021): Another massive redesign, completely different codebase, new UI, cloud integration.

Is Windows 11 the "same" operating system as Windows 1.0?

• Spatiotemporal Continuity: Yes, it has continuously evolved, with a clear lineage and continuous updates over time. It didn't disappear and reappear.
• Functionalism: Yes, its core function remains to provide an operating system for personal computers. The features have changed dramatically, but its purpose is continuous.
• Substance/Continuity: This one's tricky. The literal code (substance) has been almost entirely replaced. If we define "substance" as the actual lines of code, then no. But if "substance" refers to the project or the brand, then yes, it's continuous.
• Bundle Theory: If "Windows" is a bundle of specific features and UI elements, then Windows 11 is a very different bundle than Windows 1.0. This theory would lean towards them being different.

In practice, most people would say "Windows 11 is still Windows" because of its historical lineage, brand identity, and continuous functionality, aligning with spatiotemporal continuity and functionalism.

4. Key Takeaways

• Identity over time questions how something remains "itself" despite changes.
• The Ship of Theseus thought experiment is the classic illustration of this problem.
• Spatiotemporal continuity emphasizes an unbroken existence through space and time.
• Functionalism links identity to an object's purpose or role.
• Substance/Continuity theory looks for an enduring core or causal chain.
• Bundle theory sees identity as a collection of properties, which can change.
• For people, psychological continuity (memory, personality) is a key theory.

Common Mistakes to Avoid:
- Don't assume there's one "right" answer; these are philosophical debates.
- Don't confuse the components of an object with its identity as a whole.
- Don't apply theories like psychological continuity to inanimate objects.
- Don't overlook the role of context – sometimes "sameness" is culturally or practically defined.

5. Now Try It

Think about your local sports team. Over decades, every player, coach, and even the stadium might have changed. Is it still the "same" team? Apply at least three different theories of identity over time (e.g., Spatiotemporal Continuity, Functionalism, Bundle Theory) to argue both for and against it being the same team. Your success will be demonstrating how each theory leads to a potentially different conclusion.