Picture a thing, any particular thing. Is it still the same thing if all of its parts are gradually replaced? This ancient question, known as the Ship of Theseus paradox, was the subject of a fascinating conversation between Robert J. Marks and Walter Myers on a recent Mind Matters podcast.

Myers, a principal engineering manager at Microsoft and a philosophy graduate from Biola University, explained the centuries-old thought experiment. In Greek mythology, the Athenians are said to have preserved and maintained the ship of the hero Theseus, replacing worn parts piece by piece over the years. Eventually, none of the original parts remained. The question naturally followed: was it still the same ship?

The paradox can be elaborated. In the 17th century, philosopher Thomas Hobbes (1588-1679) added a twist: what if all the discarded original pieces were collected and reassembled into another ship? Which one, then, is the real Ship of Theseus — the restored original or the continuously maintained version? This very short video illustrates the twist version:

Why the puzzle matters

This seemingly abstract puzzle touches directly on the nature of personal identity. Our own bodies are constantly replacing cells. Skin, gut, liver, and even parts of our skeleton regenerate over time. Neurons in the brain are an exception, but by old age, much of the physical body is materially different from the younger one.

Are we still the same person as at age ten? Myers explained that in philosophy, this is known as the problem of personal identity over time. One solution he pointed to is the Continued Identity Theory — as long as change happens gradually and there’s continuity of experience, identity remains intact.

Where dualism comes in

But Myers, drawing from Aristotle, takes the discussion even deeper. He sees the human being as a unity of both body and soul (hylomorphic dualism). Hylomorphic dualism differs from substance dualism, the type that sees body and soul as two separate things. Rather, hylomorphism teaches that body and soul together form a single, unified substance. The soul gives form and purpose to the body — it “informs” the body, animating it and allowing it to carry out distinctly human activities like thought, love, and creativity.

This hylomorphic view has profound implications. Even if every part of your body were replaced at the atomic level, Myers argues, you would still be you — provided your memories, personality, and experiences continued. But a perfect physical copy or clone would not be the same you, because it would lack your soul, your history, and your continuity of existence.

How it plays out in science fiction — and life

The conversation turned to science fiction — like the famous Star Trek episode where Captain Kirk is duplicated in a transporter accident. If a copy has all the same memories and physical features, is it the same person?

Myers sees this scenario as highlighting the limits of materialism. Humans, he says, are more than just collections of physical parts or “meat computers.” We are embodied souls.

The Ship of Theseus puzzle also plays out in everyday life. Marks pointed out that companies, like Disney, change dramatically over time — employees come and go, policies shift, yet the brand persists. Similarly, in the art world, the value of the original Mona Lisa far exceeds any perfect replica, because of its unique history and connection to Leonardo da Vinci himself.

In the end, Myers suggests that these debates often hinge on how we define sameness and identity. Are we focusing on material composition, function, continuity, or something deeper? The Ship of Theseus forces us to ask: what really makes something — or someone — the same over time?

For Myers, it comes back to the soul

In his view, the soul is what ultimately grounds human identity. It’s why humans are different from machines, animals, or rocks. And while science can measure cells and neurons, it cannot fully explain love, creativity, or understanding — those immaterial aspects of being human that point to something beyond the merely physical.

As Marks concluded, that’s what makes questions like the Ship of Theseus not just fun puzzles, but windows into some of life’s deepest mysteries.